Abstract: In this paper, we consider the problem of quantifying parametric uncertainty in classical empirical interatomic potentials (IPs) using both Bayesian (Markov Chain Monte Carlo) and frequentist (profile likelihood) methods. We interface these tools with the Open Knowledgebase of Interatomic Models and study three models based on the Lennard-Jones, Morse, and Stillinger-Weber potentials. We confirm that IPs are typically sloppy, i.e., insensitive to coordinated changes in some parameter combinations. Because the inverse problem in such models is ill-conditioned, parameters are unidentifiable. This presents challenges for traditional statistical methods, as we demonstrate and interpret within both Bayesian and frequentist frameworks. We use information geometry to illuminate the underlying cause of this phenomenon and show that IPs have global properties similar to those of sloppy models from fields, such as systems biology, power systems, and critical phenomena. IPs correspond to bounded manifolds with a hierarchy of widths, leading to low effective dimensionality in the model. We show how information geometry can motivate new, natural parameterizations that improve the stability and interpretation of uncertainty quantification analysis and further suggest simplified, less-sloppy models. read less

Abstract: The effect of the size of nickel nanoparticles on the fabrication of a Ni–graphene composite by hydrostatic pressure at 0 K followed by annealing at 1000 and 2000 K is studied by molecular dynamics simulation. Crumpled graphene, consisting of crumpled graphene flakes interconnected by van der Waals forces is chosen as the matrix for the composite and filled with nickel nanoparticles composed of 21 and 47 atoms. It is found that the main factors that affect composite fabrication are nanoparticle size, the orientation of the structural units, and temperature of the fabrication process. The best stress–strain behavior is achieved for the Ni/graphene composite with Ni47 nanoparticle after annealing at 2000 K. However, all of the composites obtained had strength property anisotropy due to the inhomogeneous distribution of pores in the material volume. read less

Abstract: We calculate the degree to which the final structure of the local groundstate in a liquid is a function of the strength of a perturbing potential applied during energy minimization. This structural susceptibility is shown to correlate well with the observed tendency of the liquid adjacent to a crystal interface to exhibit a crystalline groundstate, a feature that has been strongly linked to the observation of ultra-fast crystal growth in pure metals and ionic melts. It is shown that the structural susceptibility increases dramatically as the interaction potential between atoms is softened. read less

Abstract: In this study, using the Green-Kubo-method-based molecular dynamics simulations, correlations for predicting the thermophysical properties of nanofluids are developed based on particle shape, fluid temperature, and volume concentration. Silver nanofluids with various nanoparticle shapes including spheres, cubes, cylinders, and rectangular prisms are investigated. The numerical study is conducted within the concentration range 0.14-1.4 vol % and temperature range 280-335 K. The relative thermal conductivity and relative viscosity predicated by the proposed correlations are within a mean deviation of 2% and 5%, respectively, as compared with the experimental results from this study and the available literature. The proposed correlation will be a useful tool for engineers in designing the nanofluids for different applications in industry. read less

Abstract: Thermodynamic properties and anharmonic effects in X-ray absorption fine structure (XAFS) have been studied based on the anharmonic correlated Debye model Debye–Waller factors presented in terms of cumulant expansion. The derived analytical expressions of three first XAFS cumulants involve more information on phonon-phonon interactions taken from integration over the first Brillouin zone. Many-body effects are taken into account in the present one-dimensional model based on the first shell near neighbor contributions to the vibrations between absorber and backscatterer atoms. Morse potential is assumed to describe single-pair atomic interaction included in the derived anharmonic interatomic effective potential. The present theory can be applied to any crystal structure including complex systems. Numerical results for Cu and Ni are found to be in good agreement with experiment and with those of the other theories. read less

Abstract: Three-dimensional (3D) integration technology using Cu interconnections has emerged as a promising solution to improve the performance of silicon microelectronic devices. However, Cu diffuses into SiO2 and requires a barrier layer such as Ta to ensure acceptable reliability. In this paper, the effects of temperature and strain normal to the interface on the inter-diffusion of Cu and Ta at annealing conditions are investigated using a molecular dynamics (MD) technique with embedded atomic method (EAM) potentials. Under thermal annealing conditions without strain, it is found that a Cu-rich diffusion region approximately 2 nm thick is formed at 1000 K after 10 ns of annealing. Ta is capable of diffusing into the interior of Cu but Cu hardly diffuses into the inner lattice of Ta. At the Cu side near the interface an amorphous structure is formed due to the process of diffusion. The diffusion activation energy of Cu and Ta are found to be 0.9769 and 0.586 eV, respectively. However, when a strain is applied, a... read less

Abstract: In this study, molecular dynamics (MD) are used to simulate the nanoimprinting behaviors of Ag thin films with impurities using a cuboid diamond punch. The results of the simulation show that the imprinting topography of Ag thin films depends on the slip behaviors of dislocations. In the punch indenting process, dislocations would be interfered by impurities defects. In the drafting process, the forming holes appear spring back and micro plastic recovery phenomenon, and the impurities affect the both behaviors. Although the impurities can result in a bigger springback, a better surface roughness can be obtained. read less

Abstract: This study investigates the effect of precipitate interfacial bonding strength on the mechanical behavior of Fe nanowire (NW) under simple tension in the [110] direction by molecular dynamic simulation. The results thus obtained that the weak bonding of interface between the precipitate and the Fe nanowire gets a void that was formed close to the precipitate in the tensile process, and plastic deformation occurred mostly close to the precipitate. Additionally, dislocations cannot shear off the hard precipitate, resulting in gradual void growth. Finally, the nanowire broke down around the precipitate and void. In case of high strength bonding of interface between the precipitate and the Fe nanowire, the dislocations can shear off the precipitate, blocking the motion of the dislocation, increasing precipitation strengthening. read less

Abstract: The structures of the Si/Cu heterogenous interface impacted by a nanoindenter with different incident angles and depths are investigated in detail using molecular dynamics simulation. The simulation results suggest that for certain incident angles, the nanoindenter with increasing depth can firstly increase the stress of each atom at the interface and it then introduces more serious structural deformation of the Si/Cu heterogenous interface. A nanoindenter with increasing incident angle (absolute value) can increase the length of the Si or Cu extended atom layer. It is worth mentioning that when the incident angle of the nanoindenter is between −45° and 45°, these Si or Cu atoms near the nanoindenter reach a stable state, which has a lower stress and a shorter length of the Si or Cu extended atom layer than those of the other incident angles. This may give a direction to the planarizing process of very large scale integration circuits manufacture. read less

Abstract: A previously developed steady‐state statistical sputtering model (SS‐SSM) is useful for interpretation of molecular dynamics (MD) simulations of repetitive bombardment. This method is applicable to computer modeling of depth profiling. In this paper, we demonstrate how the formalism provided by SS‐SSM is used to identify the factors that determine the depth resolution of δ‐layer depth profiling. The analysis is based on MD simulations of repetitive keV C60 bombardment of coinage metal samples. The results show that the primary dependence of the depth profiling quality is on the sample binding energy, with bigger binding energies giving better depth resolution. The effects of sample atom mass and surface opacity are also discussed. Copyright © 2014 John Wiley & Sons, Ltd. read less

Abstract: Among the carbon allotropes newly discovered during the last few decades, carbon nanotubes (CNTs) have attracted enormous attention due to their structural and electronic properties with strong one dimensional character. The physical and chemical features of such systems are intrinsically rich and complex, and can only be probed by using multiple experimental and theoretical techniques. In this feature, we focus on the structural and electronic properties of CNTs that can be accessed by using transmission electron energy loss spectroscopies. The latter are complementary to optical and X-ray absorption techniques, yet allow to obtain the electronic structure with nanoscale spatial resolution. An improved understanding of the structure-electronic properties relationship of these unique 1D systems would represent a fundamental advance, and holds the promise of using CNTs in future applications. read less

Abstract: Molecular dynamics simulations were used to investigate the effect of epitaxial ordering of the fluid molecules on the microscopic dynamic contact angle. The simulations were performed in a Couette-flow-like geometry where two immiscible fluids were confined between two parallel walls moving in opposite directions. The extent of ordering was varied by changing the number density of the wall particles. As the ordering becomes more evident, the change in the dynamic contact angle tends to be more sensitive to the increase in the relative velocity of the contact line to the wall. Stress components around the contact line is evaluated in order to examine the stress balance among the hydrodynamic stresses (viscous stress and pressure), the deviation of Young's stress from the static equilibrium condition, and the fluid-wall shear stress induced by the relative motion between them. It is shown that the magnitude of the shear stress on the fluid-wall surface is the primary contribution to the sensitivity of the dynamic contact angle and that the sensitivity is intensified by the fluid ordering near the wall surface. read less

Abstract: The high frequency phonon properties of a computer-generated nanocrystalline (nc) Ni are investigated by directly calculating the onsite phonon Green function using a recursion technique based on a continued fraction representation. Past work found that a high frequency enhancement of the vibrational density of states exists and arises from localised vibrational modes forming within the nc grain boundary regions at atoms of reduced coordination [Phys. Rev. Lett. 92 (2004) p.035505]. In the present work, the positron wave function for such nanocrystalline grain boundaries was calculated and used to identify regions of localised free volume that, in turn, were found to correlate well with the localised vibrational modes. The work also demonstrates that, irrespective of the form of the central-force inter-atomic potential used, the observed effect can be more generally understood with respect to local variations in hydrostatic pressure within the grain boundary. read less

Abstract: Simulations of nanoindentation into a typical optical-coatings stack employed in energy efficient glazing have been performed using classical molecular dynamics (MD) and a coupled finite element/MD methodology. The coatings stack consists of a low-emissivity material, Ag, sandwiched between two layers of a transparent conducting oxide (TCO), ZnO. Simulations into both the ZnO and the coatings stack show a strong interaction between the tip symmetry and crystal symmetry in the observed displacement field. A large amount of elastic recovery is observed for both the ZnO system and the coatings stack, but with an impression left on the surface that looks like a crack but extends no further than the tip imprint at maximum depth. The full stack is observed to have a lower hardness once there is a significant penetration of the displacement field into the Ag, when compared to the pure ZnO system. A comparison between the coupled finite element/MD methodology and the fixed boundary MD-only model shows that the boundary conditions have little influence on the calculated results. read less

Abstract: The mechanisms of nickel thin films irradiated by femtosecond laser pulse trains are studied by a model using molecular dynamics simulations and two-temperature model. It is found that the pulse train technology can change energy transport and corresponding phase change processes. Compared with single pulse ablation at the same total fluence, the pulse trains lead to (1) lower ablation rate with more and smaller uniform nanoparticles, (2) higher film surface temperatures and longer thermalization time, (3) much lower electron thermal conductivity that can further control heat-affected zone, (4) significantly smaller film compressive stresses and tensile stresses which reduce microcracks, and (5) a transition from phase explosion to the critical point phase separation which favors small uniform nanoparticle generation. read less

Abstract: We compare the local order in single-wall carbon nanotubes (SWCNTs) and highly oriented pyrolitic graphite (HOPG) by means of nanoscale transmission extended energy loss fine structure (EXELFS) measurements above the carbon K edge. The HOPG EXELFS spectra and their Fourier transform were compared to their synchrotron extended X-ray absorption fine structure (EXAFS) counterpart and discussed within a multiple scattering framework. By comparing the experimental EXELFS data to spectra calculated using a theoretical model based on a single scattering approach, we showed the fundamental importance of considering multiple paths (involving up to eight body scattering) to reproduce the fine details of EXELFS features. Simulating EXELFS spectra of SWCNTs by our theoretical model is shown to represent a measure of their chiralities. Finally, the shrinkage of the nearest-neighbor distance in the Fourier transform observed for SWCNTs (absent in graphite) is interpreted within a simple model invoking anharmonic effects. read less

Abstract: We use dislocation theory and molecular dynamics (MD) simulations to investigate the effect of atom properties on the macroscopic strain rate sensitivity of fcc metals. A method to analyse such effect is proposed. The stress dependence of dislocation velocity is identified as the key of such study and is obtained via 2-D MD simulations on the motion of an individual dislocation in an fcc metal. Combining the simulation results with Orowan's relationship, it is concluded that strain rate sensitivities of fcc metals are mainly dependent on their atomic mass rather than the interatomic potential. The order of strain rate sensitivities of five fcc metals obtained by analysing is consistent with the experimental results available. read less

Abstract: Kuramoto et al. calculated the activation energy for dislocation loop migration by integrating the force-distance curve. Their method has a great potential for the determination of migration energy in many cases. However, the validity of the application of their method to point defect migration has not yet been proved, because the migration of point defects is a thermally activated process and the physical meaning of the force in the force-distance curve has not been clarified. In this study, the validity was investigated by three methods to calculate the vacancy migration energy. In the first method, the migration energy was obtained by definition from the difference in potential energy between the equilibrium configuration before migration and the saddle point configuration (Method 1) using a statistic lattice relaxation method. The second method involved a molecular dynamics simulation based on an absolute reaction rate theory (Method 2). The third method involved the integration of the force-distance curve obtained by the statistic lattice relaxation method mentioned above (Method 3). The calculation model used was a two-dimensional hexagonal lattice and the Morse potential for Cu was used. The migration energies obtained by Methods 1, 2 and 3 were 0.391 eV, 0.394 ± 0.009 eV and 0.392 eV, respectively. As these values were similar, the validity of Method 3 was demonstrated. read less

Abstract: Laser ablation of Al, Ni, Fe, and Cu was investigated for pulse durations of 0.1, 1 and 5 ps at fluences up to 100 J.cm-2. The ablation depth per pulse was measured and the ablation thresholds were estimated. The increase of the pulse duration results in a decrease of the ablation rate. The presence of a molten phase is clearly expressed at fluences above 10 J.cm-2. Molecular Dynamics simulation was used to model the laser ablation process in the case of Fe, Al and Ni. read less

Abstract: We used time-gated optical emission spectroscopy to investigate the characteristics of aluminum plumes and their vacuum expansion after femtosecond laser ablation at different fluences. The prominent feature is the presence of two main classes of species in the plume: very fast Al atoms and ions preceding the plume bulk essentially constituted of much slower Al nanoparticles expanding with a ten times smaller average velocity. Atomic force microscopy of deposited Al nanoparticles evidenced an average size of about 10nm with a pretty narrow size distribution. These results and the peculiar feature of nanoparticle formation during femtosecond laser irradiation of matter were very satisfactorily interpreted and reproduced by molecular-dynamics simulation of the process. Finally, the analysis of the dependence on laser fluence of the ablation process showed an initial logarithmic increase of ablation yield, up to about 500mJ∕cm2, followed by a sudden and very steep increase at higher fluences. According to ou... read less

Abstract: In order to better understand the mechanisms of tungsten (W) film delamination from the silicon (Si) substrate, a three-dimensional molecular dynamics (MD) simulation is being conducted to investigate the formation of residual stress during the film deposition process. For the purpose of simplicity, a Morse pair potential is proposed in this paper to simulate the interactions between W and Si atoms during the film deposition process. It appears from numerical solutions that the residual stress field in the W film is very sensitive to the W–Si interfacial potential model proposed for the MD simulation. By calibrating the controlling parameters in the interfacial potential model using the comparison between the simulated stresses and experimental data, the film stress transition from tension to compression during the film deposition process could be qualitatively simulated via the proposed simulation procedure. The numerical results presented in this paper provide a better insight into the effect of interfacial atomic potential on the stress transition in thin films. In addition, it can be seen from the MD simulation that there might exist a phase transition from the crystalline Si to amorphous W–Si structure to crystalline W around the interface area. Well-designed experiments are required to verify the simulation results. read less

Abstract: A bottleneck for multitimescale thermally activated dynamics is the computation of the potential energy surface. We explore the use of genetic programming GP to symbolically regress a mapping of the saddlepoint barriers from only a few calculated points via molecular dynamics, thereby avoiding explicit calculation of all barriers. The GP-regressed barrier function enables use of kinetic Monte Carlo to simulate real-time kinetics seconds to hours based upon realistic atomic interactions. To illustrate the concept, we apply a GP regression to vacancy-assisted migration on a surface of a concentrated binary alloy from both quantum and empirical potentials and predict the diffusion barriers within 0.1% error from 3% or less of the barriers. We discuss the significant reduction in CPU time 4 to 7 orders of magnitude, the efficacy of GP over standard regression, e.g., polynomial, and the independence of the method on the type of potential. read less

Abstract: Nanometric cutting of single-crystal materials at conventional cutting speeds (5 m s−1) is simulated for the first time using a new Monte Carlo method that is applicable to systems that are neither canonical nor microcanonical. This is accomplished by defining a local temperature in the cutting zone using the thermal analysis developed by Komanduri and Hou for conventional machining. Extension of this method to the nanometric regime permits an accurate estimate of the local temperature in cutting. This temperature is then employed in the Boltzmann probability distribution function that is used to determine the acceptance–rejection of Monte Carlo moves in the simulation. Since cutting speed is closely related to cutting temperature, the cutting speed enters the calculation via the thermal analysis equations. The method is applied to nanometric cutting of single-crystal aluminium with the crystal oriented in the (001) plane and cut in the [100] direction. Three positive rake cutting tools, namely 10°, 30° and 45°, are employed to investigate the effect of the rake angle on the forces, the specific energy and the nature of the chip formation. The method is evaluated by direct comparison with corresponding molecular dynamics simulations conducted under the same conditions. read less

Abstract: Nanometric uniaxial tension tests have been conducted on four fcc metals, namely, Al, Cu, Ag and Ni using combined Monte Carlo (MC)-damped trajectory (DT) simulations and the results compared with conventional MD simulations employing the same potential-energy surface and identical testing conditions. The MC-DT method combines DTs or steepest-descent methods with MC-Markov chains to converge the lattice atom coordinates rapidly to those that characterize the equilibrium state for a given extension of the workpiece in the tensile test. The computational times required for the MC-DT method are significantly less than the corresponding times for pure MD simulations; they are nearly a linear function of the number of lattice atoms for the MC-DT calculation, but exponential for the MD studies. This differential becomes significant as the number of atoms under consideration increases. Ultimate strengths and the corresponding strains, Young's modulus, and the strain at fracture are nearly in the same ranking order as the intrinsic strength and ductility of these materials and agree reasonably well with the theoretical strength calculations as well as with pure MD simulations. read less

Abstract: Temperature dependencies of Ni, Cu and Mo metals EXAFS spectra were studied in order to determine the anharmonic pair potential. The potential parameters for metals with cubic structure - Ni, Cu, Mo as well as for Pb (Stern?E?A et al 1991 Phys. Rev. B 43 8850), Au, Ag (Newville?M and Stern?E?A http://krazy.phys.washington.edu/paper/ag-au.html) - obtained earlier, were analysed to find correlations with other physical characteristics. It was found that a, b potential parameter values correlate with cohesive energy and interatomic distance for face-centred-cubic structure metals. Obtained potential parameter values were used to determine thermodynamics parameters, including the linear coefficient of thermal expansion, the Debye temperature, the bulk modulus and the Grunesien parameter. read less

Abstract: A molecular dynamics simulation was conducted on hydrogen embrittlement at a crack tip of a single crystal of -iron composed of {100} planes under uniaxial tensile load along the 100 direction on a nanometre scale at 293 K. The modified Morse pair-potential function of Fe-Fe and the Morse potential function of Fe-H were used to calculate the interatomic action force. A three-dimensional model with 2618 iron atoms and from one to 260 hydrogen atoms segregated at the notched area was designed for the simulation. The general conclusion on hydrogen embrittlement of a single crystal of -iron could be described qualitatively as the processes of cavity nucleation, cavity linkage and, finally, fracture. Cavity nucleation occurs on the (100) plane in the notched area of the specimen with more than three hydrogen atoms at the early stage of the deformation and does not depend on the hydrogen content. The cavities are linked to each other and fracture occurs on the plane with progressing deformation. The deformation step of cavity linkage and fracture decrease logarithmically with increasing hydrogen content, while neither the cavity nor the fracture occur, even at the maximum total deformation of 50%, due to blunting of the crack tip in the specimen without hydrogen. read less

Abstract: Several molecular dynamics simulations are performed, in order to clarify the atomic-scale stick-slip phenomenon which is commonly observed in the surface measurement using an atomic fine microscope (AFM). In the molecular dynamics simulations, a specimen and a slider are assumed to consist of monocrystalline copper and rigid diamond, respectively, and a Morse potential is postulated between a pair of atoms. Atomic behavior in a plane corresponding to the (111) crystal plane is simulated, dealing with a planar strain problem where the effect of the three-dimensional interatomic force and the spring constant of the AFM cantilever are also taken into consideration. Influence of the cantilever stiffness and dynamics of the specimen surface atoms on the atomic-scale stick-slip phenomenon are investigated. The simulation confirms that the atomic-scale stick-slip phenomenon can be expressed by a molecular dynamics simulation and that the stick-slip phenomenon of the surface atoms of the specimen affects the stick-slip phenomenon of the spring force. These results indicate that molecular dynamics simulation has an advantage in deciding the spring constant of cantilevers. read less

Abstract: The effective interaction potential for tungsten is used to calculate the second moment of phonon spectrum, , Debye temperature, and cohesive properties. It is shown that the potentials obtained give good agreement of cohesive properties with the data calculated from the universal function of Rose et al. The applicability of the atomic sphere approximation to the calculation of the integral thermodynamic properties of tungsten is discussed. The convergence of in real space is studied; we find that the main contribution to is given by the first coordination shell. The Gibbs–Bogoliubov inequality and the variational procedure of Ross are used to calculate the temperature dependence of free energy in liquid tungsten. The thermodynamic functions obtained for solid and liquid phases are employed in determination of the melting temperature. © 1995 John Wiley & Sons, Inc. read less

Abstract: The method of molecular dynamics is used to study the mechanism governing crack growth in two-dimensional crystals at low and high temperatures. It is shown that at low temperatures and small strains the fracture is due to fluctuations breaking interatomic bonds in the crack tip. At large strains the fracture becomes a three-stage process which is connected with dislocation emission, cleavage of dislocation cores, and nucleation of new cracks. Die Methode der Molekulardynamik wird benutzt, um den das Riswachstum in zweidimensionalen Kristallen bei niedrigen und hohen Temperature bestimmenden Mechanismus zu untersuchen. Es wird gezeigt, das bei niedrigen Temperaturen und kleinen Spannungen der Bruch durch Fluktuationen, die interatomare Bindungen an der Risspitze aufbrechen, hervorgerufen wird. Bei grosen Spannungen geht der Bruch in einen Drei-Stufenprozes uber, der mit Versetzungsemission, Spalten von Versetzungskernen und Bildung neuer Riskeime verbunden ist. read less

Abstract: A temperature sequence of EXAFS measurements was carried out on a highly dispersed Pt/SiO2 catalyst to determine the temperature dependence of atomic structure in the very small supported clusters. A one‐shell EXAFS model was fit to the first neighbor oscillations in the catalyst data to determine bond lengths and relative thermal motion (disorder) for an average cluster environment. A Debye model of disorder was employed in the EXAFS analysis. The disorder measured for the catalyst was determined to be 1.3 to 2 times the value determined for bulk Pt over all temperatures. Asymmetry of the radial distributions of nearest neighbors in the largely surface coordinated clusters and the increased atomic disorder lead to underestimates of the nearest‐neighbor distance R1 at higher temperatures. The apparent bond distance contraction with temperature is manifest in the data as a retardation in the phase of the first neighbor oscillations. It is demonstrated that model EXAFS functions employing asymmetric interat... read less

Abstract: In order to better understand the mechanisms of tungsten (W) film delamination from the silicon (Si) substrate, a three-dimensional molecular dynamics (MD) simulation is being conducted to investigate the formation of residual stress during the film deposition process. For the purpose of simplicity, a Morse pair potential is proposed in this paper to simulate the interactions between W and Si atoms during the film deposition process. It appears from numerical solutions that the residual stress field in the W film is very sensitive to the W–Si interfacial potential model proposed for the MD simulation. By calibrating the controlling parameters in the interfacial potential model using the comparison between the simulated stresses and experimental data, the film stress transition from tension to compression during the film deposition process could be qualitatively simulated via the proposed simulation procedure. The numerical results presented in this paper provide a better insight into the effect of interfacial atomic potential on the stress transition in thin films. In addition, it can be seen from the MD simulation that there might exist a phase transition from the crystalline Si to amorphous W–Si structure to crystalline W around the interface area. Well-designed experiments are required to verify the simulation results. read less

Abstract: γ-TiAl alloy is one of the most potentially lightweight and high-temperature structural materials, and its machined surface quality has a significant effect on member service performance. Despite the extensive research on plastic removal and defect evolution under different cutting parameters, the forming mechanism of surface topography is not perfect under different cutting parameters. It is necessary to study the variation law of surface topography under the influence of different cutting parameters from the atomic scale. To this end, the influence of cutting depths and cutting speeds on the machined surface topography is investigated during nano-cutting of polycrystalline γ-TiAl alloys based on molecular dynamics simulation methods, and the effect of defective grain boundaries on cutting force fluctuations is analyzed. The results show that the effect of grain boundary on material deformation and dislocation obstruction is the main reason for the peak cutting force; with the increase of cutting depth, the average cutting force and friction coefficient increase, and both Sa and Sq show an increasing trend, which is the result of the joint action of plowing effect and grain boundary distribution; Sa and Sq show a decreasing and then increasing trend with the increase of cutting speed, and the critical cutting speed is 200 m s−1. This indicates that a smaller cutting depth and an appropriately higher cutting speed can effectively improve the surface quality of the polycrystalline γ-TiAl alloy, and optimize its nano-cutting process. read less

Abstract: In this work, the method of fabrication of the composites based on a graphene network and metal nanoparticles (Ni and Al) by deformation-heat treatment is considered by molecular dynamics simulation. A graphene network filled with Al or Ni nanoparticles are considered to study the fabrication of the composites and their mechanical properties. The diameter of Ni and Al nanoparticle is 6.2 and 7.5 Å, while in the final composite state, the ratio of metal and carbon atoms in the graphene/Al and graphene/Ni systems are 8 and 7.7 at.%, respectively. It is shown that hydrostatic compression is an effective way to obtain graphene/metal composites. In the compressed structure (composite state) no pores are found since compression is conducted to the maximum possible density. It is found that the graphene/Ni composite has better mechanical properties in comparison with the graphene/Al composite. The enhanced mechanical properties of the graphene/Ni composite are explained by the formation of a graphene network of high strength with metal nanoparticles uniformly distributed over the graphene pores. It has been established, that in the graphene/Al composite, both during hydrostatic and uniaxial tension, due to its low cohesion energy with graphene, metal nanoparticles begin to coagulate, which is more energetically favorable. The larger Al nanoparticles that appear in the structure are the weak places of the composite, where the fracture of the composite occurs most easily. read less

Abstract: γ-TiAl alloys are the most promising lightweight high-temperature structural materials, but the materials often fail from the surface, which is mainly attributed to the stress state of the material surface. In this paper, the orthogonal experiment method and molecular dynamics modeling are used to choose a set of the best process parameters for supersonic fine particle bombardment (SFPB). Furthermore, by determining the optimal process parameters, this study examines the influence of residual stress distribution on the mechanical properties of the material under various process conditions. The simulation results reveal that the residual stress distribution is minimally impacted by particle radius, nonetheless, maintaining a moderate level of compressive residual stress within a specific range can substantially augment both the tensile strength and indentation hardness. An increase in the number of particles results in a more uniform distribution of surface residual stresses. Conversely, an increase in the number of impacts causes stress concentration to intensify at the particle’s contact point, and thus a deeper distribution of residual stress is observed. This study illustrates how the mechanical properties of polycrystalline γ-TiAl alloy are affected by the process parameters of SFPB in terms of atomic size in order to develop and select the optimal SFPB parameters. read less

Abstract: Molecular dynamics simulation is used to study and compare the mechanical properties obtained from compression and tension numerical tests of multilayered graphene with an increased interlayer distance. The multilayer graphene with an interlayer distance two-times larger than in graphite is studied first under biaxial compression and then under uniaxial tension along three different axes. The mechanical properties, e.g., the tensile strength and ductility as well as the deformation characteristics due to graphene layer stacking, are studied. The results show that the mechanical properties along different directions are significantly distinguished. Two competitive mechanisms are found both for the compression and tension of multilayer graphene—the crumpling of graphene layers increases the stresses, while the sliding of graphene layers through the surface-to-surface connection lowers it. Multilayer graphene after biaxial compression can sustain high tensile stresses combined with high plasticity. The main outcome of the study of such complex architecture is an important step towards the design of advanced carbon nanomaterials with improved mechanical properties. read less

Abstract: The plastic deformation behavior and microstructural changes in workpieces during ultra-precision machining have piqued the interest of many researchers. In this study, a molecular dynamics simulation of nano-cutting iron-carbon alloy (α-Fe) is established to investigate the effects of the fluid medium and cutting angle on workpiece temperature, friction coefficient, workpiece surface morphology, and dislocation evolution by constructing a molecular model of C12H26 as a fluid medium in the liquid phase using an innovative combined atomic approach. It is demonstrated that the presence of the fluid phase reduces the machining temperature and the friction coefficient. The cutting angle has a significant impact on the formation of the workpiece’s surface profile and the manner in which the workpiece’s atoms are displaced. When the cutting angle is 0°, 5°, or 10°, the workpiece’s surface morphology flows to both sides in a 45° direction, and the height of atomic accumulation on the workpiece surface gradually decreases while the area of displacement changes increases. The depth of cut increases as the cutting angle increases, causing greater material damage, and the presence of a fluid medium reduces this behavior. A dislocation reaction network is formed by the presence of more single and double-branched structures within the workpiece during the cutting process. The presence of a fluid medium during large-angle cutting reduces the number of dislocations and the total dislocation length. The total length of dislocations inside the workpiece is shorter for small angles of cutting, but the effect of the fluid medium is not very pronounced. Therefore, small cutting angles and the presence of fluid media reduce the formation of defective structures within the workpiece and ensure the machining quality. read less

Abstract: Interatomic interaction potentials are compared using a molecular dynamics modeling method to choose the simplest, but most effective, model to describe the interaction of copper nanoparticles and graphene flakes. Three potentials are considered: (1) the bond-order potential; (2) a hybrid embedded-atom-method and Morse potential; and (3) the Morse potential. The interaction is investigated for crumpled graphene filled with copper nanoparticles to determine the possibility of obtaining a composite and the mechanical properties of this material. It is observed that not all potentials can be applied to describe the graphene–copper interaction in such a system. The bond-order potential potential takes into account various characteristics of the bond (for example, the angle of rotation and bond lengths); its application increases the simulation time and results in a strong interconnection between a metal nanoparticle and a graphene flake. The hybrid embedded-atom-method/Morse potential and the Morse potential show different results and lower bonding between graphene and copper. All the potentials enable a composite structure to be obtained; however, the resulting mechanical properties, such as strength, are different. read less

Abstract: Investigation of the effect of electric current on the plastic deformation mechanism of metals during the electrically-assisted machining process is significant in further improving surface properties. In this paper, the molecular dynamics (MD) method is adopted to simulate the electrically-assisted scratching process of crystal copper, obtaining and analyzing the surface morphology, potential energy change, von Mises stress distribution, and crystal defect structure evolution. The MD simulation results show that the electric current effectively expands the dislocation slip range, resulting in a larger plastic deformation zone. Meanwhile, the combined action of the electron wind forces and Joule heating causes more dislocations to proliferate and increases the dislocation density limit, enhancing the plastic deformation ability of the single-crystal copper. Furthermore, the electric current strengthens the dislocation-grain boundary interactions and reduces the hindering effect of the grain boundaries on dislocations, promoting more dislocations to cross the grain boundaries. This work will be helpful for guiding the optimization of surface strengthening techniques to get better surface properties of metals. read less

Abstract: Molecular dynamic simulation is used to simulate the corrosion process of Fe or Ni in liquid Cs by Large-scale Atomic/Molecular Massively Parallel Simulator. The embedded-atom method potential is used to describe the interaction of Fe–Fe, Ni–Ni, and Cs–Cs, and Morse two-body potential is used to describe the Fe–Cs and Ni–Cs atomic interaction. Temperature is considered as a critical condition in this work. Results indicate that corrosion is easy to occur in the systems. The increase in temperature can help the process of Cs corrosion. Compared to the Ni–Cs system, the Fe–Cs system has a higher atomic concentration function. The radial distribution function shows that Cs atoms are dissolved into the substrates, but the Fe and Ni substrates are still crystalline structures. Moreover, Cs in Fe or Ni is still a liquid phase. read less

Abstract: In order to study the material removal mechanism of Fe–C alloy surfaces in the particle microcutting process, the molecular dynamics method was used to study the material deformation and removal rules during the particle microcutting process. By analyzing and discussing the particle cutting force, atomic energy, atomic displacement, lattice structure, and dislocation in the particle microcutting process under different cutting velocities, the material removal mechanism is revealed. The results show that the atomic binding energy of Fe–C alloy increases with an increase in particle cutting velocity. The cutting force of particles and atomic potential energy of the workpiece increase obviously. The accumulated strain energy and dislocation energy in the lattice increase, the lattice deformation becomes more severe, and the material is prone to plastic deformation. The atoms form atomic groups at the front of the particle and are then remove from the surface of Fe–C alloy in the form of chips. read less

Abstract: In this study, some features of molecular dynamics simulation for evaluating the mechanical properties of a Ni/graphene composite and analyzing the effect of incremental and dynamic tensile loading on its deformation are discussed. A new structural type of the composites is considered: graphene network (matrix) with metal nanoparticles inside. Two important factors affecting the process of uniaxial tension are studied: tension strain rate (5 ×10−3 ps−1 and 5 ×10−4 ps−1) and simulation temperature (0 and 300 K). The results show that the strain rate affects the ultimate tensile strength under tension: the lower the strain rate, the lower the critical values of strain. Tension at room temperature results in lower ultimate tensile strength in comparison with simulation at a temperature close to 0 K, at which ultimate tensile strength is closer to theoretical strength. Both simulation techniques (dynamic and incremental) can be effectively used for such a study and result in almost similar behavior. Fabrication technique plays a key role in the formation of the composite with low anisotropy. In the present work, uniaxial tension along three directions shows a big difference in the composite strength. It is shown that the ultimate tensile strength of the Ni/graphene composite is close to that of pure crumpled graphene, while the ductility of crumpled graphene with metal nanoparticles inside is two times higher. The obtained results shed the light on the simulation methodology which should be used for the study of the deformation behavior of carbon/metal nanostructures. read less

Abstract: The molecular dynamics method was used to study the removal mechanism of boron nitride particles by multi-angle microcutting of single-crystal copper from the microscopic point of view. The mechanical properties and energy conversion characteristics of single-crystal copper during microcutting were analyzed and the atomic displacement and dislocation formation in the microcutting process are discussed. The research results showed that during the energy transfer between atoms during the microcutting process of boron nitride particles, the crystal lattice of the single-crystal copper atom in the cutting extrusion region was deformed and displaced, the atomic temperature and thermal motion in the contact area between boron nitride particles and Newtonian layer of workpiece increased, the single-crystal copper atom lattice was defective, and the atomic arrangement structure was destroyed and recombined. The interface of different crystal structures formed a dislocation structure and produced plastic deformation. With the increase of the impact cutting angle, the dislocation density inside the crystal increased, the defect structure increased and the surface quality of the workpiece decreased. To protect the internal structure of the workpiece and improve the material removal rate, a smaller cutting angle should be selected for the abrasive flow microcutting function, which can reduce the formation of an internal defect structure and effectively improve the quality of abrasive flow precision machining. The research conclusions can provide a theoretical basis and technical support for the development of precision abrasive flow processing technology. read less

Abstract: In this work, we have developed the anharmonic Debye model to study the Debye temperature and thermal disorder in Fe-Cr intermetallic alloys. The analytical expressions of the anharmonic effective potential, the effective force constant, the Debye temperature and corresponding frequency, and the atomic mean-square displacement characterizing the Debye-Waller factor have been derived. We have implemented the numerical calculations for Fe-Cr intermetallic systems with various Cr concentration up to temperature 700 K. Our results show that the Debye temperature of Fe-Cr systems increases gradually with the increasing Cr composition. Reversely, the mean-square displacement curve drops gradually with Cr concentration. These effects can be explained by the weaker coupling force between Fe atoms as compared to the Cr atoms. Furthermore, we also show the important contributions of thermal disorder to mean-square displacement at high temperature due to thermal lattice vibrations. read less

Abstract: Ni-based alloys are widely used in aerospace because of their high strength and high temperature oxidation resistance. CBN tool is suitable for precision machining of Ni-based alloy. Diffusion wear is an important wear form of CBN tool in the process of cutting Ni-based alloy. Therefore, it is of great significance to study the diffusion phenomenon in the process of cutting Ni-based alloy with CBN tool. In this paper, the cutting model of Ni-based alloy containing γ′ phase (Ni3Al) with CBN tool is established based on the molecular dynamics (MD) simulation method. The self diffusion activation energy of all kinds of atoms in the workpiece and the formation energy of several point defects in the tool are calculated, so as to study in depth the atom diffusion mechanism according to the simulation results. The results show that the atoms in the crystal boundary of the workpiece are the most easily diffused, followed by the atoms in the phase boundary, and the atoms in the lattice are the most difficult to diffuse. When the workpiece atoms diffuse into the tool, it is easier to diffuse into the tool grain boundary than to form interstitial impurity atoms or displacement impurity atoms. It is more difficult to form the substitutional impurity atom than to form the interstitial impurity atom. read less

Abstract: By incorporating the adhesive force as a body force in the finite element method, the adhesive contact between a diamond sphere and the iron substrate is studied. The adhesive force is derived from Morse potential by integrating the pair potential function over the spherical domain. Based on the tensile behaviors of iron nanowires, the elastic and elastoplastic material parameters are obtained for the substrate. As the radius of the sphere is larger than 320 nm and the maximum depth of indentation is one-tenth of the radius of the sphere, the adhesion caused by interatomic interaction between diamond and iron is small enough to ignore. Then take the sphere whose radius is 20 nm as an example, the results of a single load–unload cycle and multiple load–unload cycles are discussed. In the contact process between the sphere and the surface, the phenomena jump-to-contact and jump-off-contact were observed. Further, the stress distributions inside the substrate and the pressure distribution are investigated. With the analysis of the results, the proposed method can be used to simulate the mechanical behaviors under micro-nano scale contact. read less

Abstract: In order to explore the evolution mechanism of subsurface defect structure of iron–carbon alloy workpiece during abrasive flow machining, the molecular dynamics model of SiC particle micro-cutting iron–carbon alloys was established. The Common Neighbor Analysis and Dislocation Extraction Algorithm were applied to identify the crystal structure and lattice defects. The distribution and evolution of defect structure during micro-cutting were analyzed and discussed, and the removal mechanism of workpiece material during micro-cutting was revealed. The results show that dislocations, stacking faults, V-shaped dislocation loops, atomic clusters, and point defect structures were generated in the subsurface layer of the iron–carbon alloy workpiece during micro-cutting. Under the action of extrusion and friction of SiC particles, some atoms in the shear slip zone were largely displaced. The plastic deformation occurred on the workpiece and formed chips and machining surfaces. Some atoms extended into the interior of the workpiece material, resulting in subsurface defect structure. After the completion of particle micro-cutting, some defect structures of the subsurface layer disappeared, and some defect structures remained in the subsurface of the workpiece in a certain form, forming a subsurface defect layer. read less

Abstract: The molecular dynamics simulation using the Morse potential has been applied to calculate the value of self-diffusion coefficients D(T) of some pure metals as Pb, Cr, Ni, and Fe. The simulation then was done using the MOLDY molecular dynamics program. The procedure to calculate these coefficients following several steps: first, determining the Morse potential parameters as D , a and r 0; second, simulating the material under consideration using Moldy based on the appropriate ensemble; third, diffusion coefficient calculation using the Green-Kubo method for specific temperature; and fourth, the temperature-dependent diffusion coefficient D(T) based on the Arrhenius. The simulation work has obtained the best results as following: for Pb metal the Morse potential parameter (a = 1.4795 A−1, r 0 = 3.733 Å, and D=0.2348eV ) with D(T)=9.68×10−9exp(−3890.79RT)[m2/s] ; for Cr metal the potential parameters ( D=0.3292eV , a = 1.1005 A−1, and r 0 = 2.2032 Å), with D(T)=1.73×10−3exp(−8725.54RT)[m2/s] ; for Ni metal the Morse potential parameter ( D=0.3784eV , a = 1.0649 A−1, r 0 = 2.085 Å), with D(T)=8.5×10−4exp(−15794.9RT)[m2/s] ; and for Fe metal the potential parameter ( D=0.4174eV , a = 1.5974 A−1, r 0 = 2.840 Å) with D(T)=4.22×10−7exp(−5878.49RT)[m2/s] . The calculated diffusion coefficients of the work have significant application as for the corrosion study of steels in nuclear reactor design. read less

Abstract: In the present work, crumpled graphene is considered under hydrostatic tension by molecular dynamics simulation. Here hydrostatic compression is used in two variants: to obtain composite from crumpled graphene combined with Ni nanoparticles and to serve hydrogen inside crumpled graphene. Pressure-strain curves and structural transformations during hydrostatic compression in both cases are discussed. It is found, that hydrostatic compression at high temperatures can be very effective for Ni-graphene composite formation. The possibility of application of compressive strain to make crumpled graphene better media for hydrogen storage is discussed. It is observed that at 77 K and 300 K compression results in the considerable increase of hydrogen sorption capacity. read less

Abstract: Fabrication of Ni-graphene composite with the nanoparticles of different sizes by hydrostatic pressure at 1500 K is studied by molecular dynamics simulation. The high specific surface area of crumpled graphene allow to fill its pores by metal nanoparticles and obtain composite structure at given conditions. It is observed, that temperature exceeding melting temperature of Ni nanoparticles but considerably lower than the melting temperature of graphene lead to better mixing of the structural elements. It is found, that one of the main factors in the composite fabrication is nanoparticle size. Bigger nanoparticles fully covered by graphene flakes even at high temperatures preserve its spherical shape and retard the obtaining of the composite structure. Nanoparticles of small and average size demonstrate the much better formation of the composite. read less

Abstract: Along with the advent of the fourth industrial revolution, the processing capacity of "big data" is highly demanded in industry community. Compared with the traditional computing and programming model based on serial program, parallel computing is based on heterogeneous architecture and runs in a completely different way from CPU, which has greatly enhanced the processing speed of large-scale data sets. Therefore, parallel computing has been developing dramatically in recent years, and has been favored by all walks of life. In the future, large-scale data processing must belong to parallel computing. Set on LAMMPS (large-scale atomic/molecular massively parallel simulator) as an example, this paper described the technique of establishing parallel computing platform, and applied it on simulated test on fracture process of lamellar structure from gas-pipeline steel. read less

Abstract: In this study, molecular dynamics (MD) are used to simulate the nanoimprinting behaviors of (001) Ni thin films using 3×3 array cuboid diamond punch. Different pitch of the punches was used to investigate the effect of the interaction among the forming pattern and the quality of the formed holes. Forming force was evaluated including normal and tractional force of the punch during pressing process. The dislocation behavior was also monitoring during the holes forming. The result showed that the pitch of the punch was 2w could get the best forming pattern. read less

Abstract: Impurity effects in Debye–Waller factors (DWFs) describing thermodynamic properties of bcc impure crystals included in X-ray absorption fine structure (XAFS) have been studied based on the anharmonic correlated Einstein model. The impurity is obtained by replacing absorber of host element by an atom of doping element. Analytical expressions of DWFs presented in terms of cumulant expansion up to the third-order and thermal expansion coefficient of impure crystals have been derived. Anharmonic effective potential of impure crystal includes interactions of absorber and backscatterer atoms with their first shell near neighbors. Morse potential is assumed to describe single-pair atomic interaction. The obtained expressions for impure crystal can also be used for calculating the considered XAFS quantities of pure material based on replacing all data of the doping atoms by those of pure host element. The advantage of using the anharmonic effective potential is shown by its possibility of defining the difference of XAFS quantities between the two inverse doping processes, which cannot be obtained by using the single-pair potential. Numerical results are found to be in good agreement with experiment for the impure Fe doped by Mo or inversely for Mo doped by Fe, as well as for pure Fe and Mo. read less

Abstract: This work investigates how the interatomic surface potential influences molecular dynamics (MD)-derived thermal accommodation coefficients (TACs). Iron, copper, and silicon surfaces are considered over a range of temperatures that include their melting points. Several classes of potentials are reviewed, including two-body, three-body, and bond-order force fields. MD-derived densities and visualization of the surfaces are used to explain the differences in the parameterizations of these potentials within the context of gas–surface scattering. Finally, TACs are predicted for a range of gas–surface combinations, and recommended values of the TAC are selected that take into account the robustness and uncertainties of each of the considered parameterizations. Further, it is observed that there is a significant change in the TAC about phase changes that must be taken into account for applications with a large range of surface temperatures. read less

Abstract: Debye-Waller factors (DWFs) of metallic Cu (fcc crystal) in X-ray absorption fine structure (XAFS) presented in terms of cumulant expansion have been studied based on the anharmonic correlated Debye model (ACDM). This ACDM is derived from the many-body perturbation approach and the anharmonic effective potential that includes the first shell near neighbor contributions to the vibration between absorber and backscatterer atoms. Analytical expressions of three first XAFS cumulants of Cu have been derived involving more information of phonon-phonon interactions taken from integration over the first Brillouin zone. Morse potential is assumed to describe the single-pair atomic interaction. Numerical results for Cu using the present ACDM show their good agreement with experiment and with those of other theories, as well as their advantages compared to those calculated using the single-pair potential. read less

Abstract: A three-dimensional molecular dynamics model is presented for the simulation of the creation of a micro-hole on a thin film metal substrate via laser ablation. For the presented analysis, molybdenum and aluminium specimens are selected and short pulses are assumed. The laser fluence takes several values between 0.5 and 20 J/cm2. The proposed models include significant laser ablation phenomena such as plasma shielding. However, they are not computationally intense. In this study, the Morse potential is used for the interactions of the atoms of the specimens. The analysis is carried out in order to investigate the ablation rate, the ablation depth and the mean temperature of molybdenum and aluminium targets under their heating by the laser beam, for several different values of fluence. Results for molybdenum indicate that as fluence increases, it takes less time for the atoms to be ablated. For low-fluence pulses, more than one pulse may be required for the ablation of all atoms. For high-fluence pulses, the ablation is not uniform across the entire duration of the pulse and the specimen is overheated. A fluence value around 2–3 J/cm2 is suggested for uniform ablation. From the analysis, it is evident that the evolution of ablation and system temperature is different for molybdenum and aluminium, for the same laser fluence. This is attributed to different crystalline structures and absorptivity of each material. It may be said that molecular dynamics prove to be a powerful tool for the simulation of nanomanufacturing processes and useful conclusions are drawn from the analysis. read less

Abstract: The mechanical properties of single and multilayer gold and copper films are studied using molecular dynamics and deformation, the slip effect, the load bearing capacity and energy differences are also discussed. Results showed that as the indentation depth increases in a multilayer model, the grain boundaries of the first layer are broken and the atoms diffuse into the lower layer, thereby leading the change of the amount of slip. Single-crystal Au and Cu models generate more slippage due to lower bond energy between atoms. The larger the amount of atomic flow under indentation is, the larger the amount of slip is. As the depth of the indentation increases, the area influenced by indentation increases and the maximum load bearing capacity and potential energy also increase. Plastic deformation from indentation at high speed does not result from dislocation slip, but from a larger force that destroys the bonds between atoms. At higher temperature, the amount of slip around the indenter is less obvious and the structure is gradually softened. Moreover, the same depth of indentation can be achieved with a smaller load force for higher temperature. read less

Abstract: Thermodynamic properties of bcc crystals have been studied based on the anharmonic correlated Debye model high-order expanded Debye-Waller factors and X-ray absorption fine structure (XAFS). The many-body effects are taken into account in the present one-dimensional model based on the anharmonic effective potential that includes interactions of absorber and backscatterer atoms with their first shell near neighbors, where Morse potential is assumed to describe the single-pair atomic interaction. Analytical expressions for dispersion relation, correlated Debye frequency and temperature and four first temperature-dependent XAFS cumulants of bcc crystals have been derived using the many-body perturbation approach. The obtained cumulants are applied to calculating XAFS spectra and their Fourier transform magnitude. Numerical results for Fe, a ferrite crystal, are found to be in good agreement with experiment. read less

Abstract: In this work, the adsorption of protein on a Au surface coated by self-assembled monolayers (SAMs) of alkanethiol chains is studied by molecular dynamics simulations with an all-atom model. Particularly, a more realistic embedded-atom method potential has been used to characterize the Au–Au interactions in the system as compared to previous studies. With this all-atom model, many experimental observations have been reproduced from the simulations. It is found that the SAMs have the lowest adsorption energy on the Au(111) surface where the alkanethiol chains form a well-ordered (√3×√3)R30° triangular lattice at 300 K. Furthermore, it is confirmed that carboxyl-terminated SAMs are more effective to absorb proteins than the methyl-terminated SAMs. On the basis of the simulation results, we propose that the experimentally observed aggregation of protein–Au nanoparticle conjugates is mainly due to the electrostatic interactions between protein amino acids and carboxyl-terminated SAMs from multiple Au surfaces. read less

Abstract: When the accuracy of the machined workpiece reaches to the nanometer scale, the atomic state in the cutting region 、 cutting force and the temperature of the workpiece newton layer must be analyzed from the atomic or molecular scale. Experiments will be difficult and time-consuming because the severe requirements of experiment for ultra-precision machine tool 、 resolution of detecting instrument and tool geometry, it becomes very difficult to study the effects of tool rake angle for nanometric cutting process and especially the workpiece temperature. Molecular dynamics simulation was used to carry out molecular dynamics modeling 、 simulation and analysis for diamond tools with different rake angle in single crystal copper surface nanometric cutting process, first of all, three-dimensional molecular dynamics simulation model of the workpiece and the tools with different rake angle were established; secondly, tools with different rake angle were used to machine the single crystal copper workpiece and calculated the CNA value of the workpiece atoms 、 the cutting force and the temperature of the workpiece newton; at last, the effect law of different tool rake angle for the atomic state in cutting region 、 cutting force variation and temperature of the workpiece newton in single crystal copper nanometric cutting process were analyzed. It was shown that when the rake angle value is negative, the increasing of temperature of workpiece newton with the increasing of the rake angle; when the rake angle value is positive, the decreasing of temperature of workpiece newton with the increasing of the rake angle. read less

Abstract: Understanding the sintering mechanism in porous anodes is necessary for developing durable anodes suitable for use in solid oxide fuel cells. A multi-nanoparticle sintering simulation method based on molecular dynamics (MD) calculation was developed for this purpose [J. Xu et al., J. Phys. Chem. C, 2013, 117, 9663–9672]. The method can be used to calculate the effect of the porous structure properties, such as the porosity and framework structure, on the sintering, unlike previous sintering simulations with conventional nanoparticle models. We revealed that, in a Ni/YSZ porous anode, the YSZ nanoparticle framework suppresses sintering of Ni nanoparticles by disrupting the growth of the neck between two Ni nanoparticles. In this paper, we used our method to reveal the effect of ceramic type on the sintering processes. We investigated the difference between the sintering and degradation processes in Ni/YSZ and Ni/ScSZ anodes. In the simulation, the degree of sintering of the Ni nanoparticles in Ni/ScSZ was smaller than that in Ni/YSZ. The stronger adhesion of Ni to ScSZ nanoparticles than to YSZ nanoparticles prevented the Ni nanoparticles from approaching each other in the Ni/ScSZ anode, inhibiting sintering. Our multi-nanoparticle sintering MD simulations revealed the different sintering processes for Ni nanoparticles in Ni/YSZ and Ni/ScSZ anodes. We also investigated the effect of sintering on degradation. The hydrogen adsorption sites and electrochemical reaction sites of the hydrogen oxidation decreased as the degree of sintering increased. A low degradation of the Ni/ScSZ anode relative to that of the Ni/YSZ anode was observed. Furthermore, we showed the effect of porosity on degradation induced by sintering in Ni/YSZ and Ni/ScSZ, and found an optimal porosity. These findings cannot be obtained by conventional two- or three-nanoparticle sintering MD simulations. Our multi-nanoparticle sintering simulation method is useful for revealing the types of ceramics suitable for inhibiting sintering and degradation in anodes, and can be used to design durable anodes. read less

Abstract: Molecular Dynamics (MD) simulations have been carried out on ultrathin Ni3Fe alloy with face-centered cubic (FCC) lattice upon application of uniaxial tension at nanolevel with a speed of 20 m/s. the deformation corresponds to the direction <001>. To the calculated block of crystal - free boundary conditions are applied in the directions <100>, <010>. Morse potential was employed to carry out three dimensional molecular dynamics simulations. A computer experiment is performed at a temperature corresponding to 300 K. MD simulation used to investigate the effect of long of ultrathin Ni3Fe alloy on the nature of deformation and fracture. The engineering stress–time diagrams obtained by the MD simulations of the tensile specimens of these ultrathin Ni3Fe alloy show a rapid increase in stress up to a maximum followed by a gradual drop to zero when the specimen fails by ductile fracture. The feature of deformation energy can be divided into four regions: quasi-elastic, plastic, flow and failure. The yield strength decreased with increasing long of alloy, but increases with increasing the cross sectional area. Plasticity disappear when the length of the allays is too large. The results showed that breaking position depended on the alloy length. read less

Abstract: The development of new materials impacts on all branches of engineering and, in particular, in aerospace engineering. Metallic glasses (MG) are relatively newcomers to the world of materials science and have excellent mechanical properties; its study is mandatory to allow its technological implantation. The macroscopic mechanical properties of a material are linked to its atomic structure. In particular, the fracture behaviour of brittle materials is initiated by the generation of vibrational modes. In metallic glasses, with amorphous structure, the vibrational spectrum has specific features. In this work, the vibrational properties of metallic glasses are examined by Molecular Dynamics simulations. The study was focused in binary systems, which were simulated using different interatomic potentials: Lennard-Jones (LJ), Morse and the semiempirical Embedded atom (EAM). As in Pd-based metallic glasses, the ratio of masses of both species was high, namely 2 in Lennard-Jones potentials and 1.67 in Morse and EAM potentials. The large scale simulations allowed us to simulate systems with nm-scale heterogeneities frozen-in during the quenching process. Different relaxation states were obtained by changing the quenching rates of the simulated MGs. The collective vibrational atomic dynamics of metallic glasses is a longstanding subject of debate. The origin of the excess of vibrational modes known as Boson Peak (BP) is not clear. In the systems analysed the dependence of the BP position and intensity on the system size is found to be weak. On the contrary, the BP intensity increases with the quenching rate, while its position shifts slightly to smaller frequencies. The results obtained by using realistic, semiempirical EAM potentials compare well with the experimental data available in glasses of similar compositions. The dynamic structure factor, S(q, ¿) is also computed in large systems to get information on the behaviour of acoustic excitations at low wavenumbers. The dominant frequencies O L,T (q) are determined for each considered wavevector, in order to compute the relation of dispersion of longitudinal and transverse phonons. In all studied cases the width of the peak, GL,T(q), increases as the frequency increases. A linear region at low wavenumbers and a bending when approaching the limit of the first pseudo-Brillouin zone are found. This behaviour is the same than that observed experimentally by Inelastic X-Ray scattering. The macroscopic sound speed is obtained for wavenumbers tending to zero. The values obtained with EAM and Morse potentials are in qualitative agreement with those obtained experimentally in systems of similar composition. The Ioffer-Regel limit (IR), where the coherence length of the phonon is similar to the phonon wavelenght, was computed. It is found that the Ioffe-Regel frequency decreases slightly when applying faster quenching rates. The longitudinal Ioffe-Regel limit was found at frequencies higher than the Boson peak frequency for all the cases, although the diference in EAM systems is much reduced. Contrary to the typical results obtained in the LJ systems, using EAM potentials in both Cu20Pd80 and Cu50Pd50 the longitudinal IR limit is very close to the position of the BP while the transversal IR limit is found well below. This behaviour is coherent with that found by IXS measurements. It is inferred that the EAM potential increases the interaction between the longitudinal modes and the BP excess states. Finally the fragility of the studied systems was obtained by calculating the viscosity at different temperatures. Lennard-Jones systems showed a much larger fragility than EAM and Morse systems. However, even systems simulated with more realistic potentials showed fragility values much higher than those obtained experimentally. This is attributed to the extremely high quenching rates used in simulations, as it is known experimentally that fragility increases with the quenching rate. El desenvolupament de nous materials té un gran impacte en totes les àrees de l'enginyeria, i en particular a l'enginyeria aeronàutica. Els vidres metàl·lics son materials relativament nous, amb excel·lents propietats mecàniques; el seu estudi és imprescindible per la seva implantació tecnològica. Les propietats mecàniques macroscòpics d'un material estan determinades per la seva estructura atòmica. En particular, la fractura de materials fràgils s'inicia per la generació de modes de vibració. Als vidres metàl·lics, d'estructura amorfa, l'espectre vibracional té característiques específiques. En aquest treball s'estudien les propietats vibracionals dels vidres metàl·lics emprant simulacions de dinàmica Molecular. L'estudi es centra en sistemes binaris simulats emprant potencials atòmics de Lennard-Jones (LJ), Morse i Embedded Atom method (EAM), de tipus semiempíric. Com als vidres metàl.lics basats en Pd, el quocient de les masses d'ambdues espècies en les simulacions és alt, essent 2 en potencials LJ i 1.67 en potencials Morse i EAM. Simulacions a gran escala permeten simular sistemes amb heterogeneities a escala nm, i la simulació a velocitats de refredament diferents permet obtenir configuracions en diferents estats de relaxació. La dinàmica de les vibracions atòmiques dels vidres metàl·lics és un tema de debat. L'origen de l'excés dels modes de vibració conegut com Boson Peak (BP) no és clar. Als sistemes analitzats s'observa que la dependència de la posició i la intensitat del BP amb la mida del sistema és feble. Al contrari, la intensitat de la BP augmenta amb la velocitat de refredament, mentre que la seva posició es desplaça a freqüències menors. Els resultats obtinguts emprant potencials de realista tipus EAM coincideixen amb les dades experimentals disponibles en vidres de composicions similars. El factor d'estructura dinàmica, S (q, ¿) es calculà també en sistemes grans per obtenir informació sobre el comportament de les excitacions acústiques en vectors d'ona baixos. També es va obtenir la relació de dispersió de fonons longitudinals i transversals. En tots els casos estudiats, l'amplada del pic, GL,T(q), augmenta amb la freqüència. S'observa una regió lineal a baixos nombres d'ona i una flexió quan s'aproxima el límit de la pseudo-zona de Brillouin. Aquest comportament és el mateix que l'observat experimentalment emprant Inelàstic X-Ray scattering (IXS). La velocitat del so macroscòpica s'obté quan el nombre d'ona tendeix a zero. Els valors obtinguts amb potencials EAM i Morse estan d'acord amb els valors mesurats experimentalment en sistemes de composició similar. El límit Ioffe-Regel (IR) es defineix com la freqüència a la que la longitud de coherència del fonó és similar a la longitud d'ona de fonó. S'observa que la freqüència IR augmenta lleugerament als sistemes més relaxats. El límit IR longitudinal és troba en tots els casos a freqüències superiors a la freqüència del BP. Contràriament als resultats obtinguts en els sistemes LJ, el límit longitudinal IR en Cu20Pd80 y Cu50Pd50 és molt a prop de la posició del BP, mentre que el límit transversal IR és molt per sota d'aquest valor; aquests resultats estan d'acord amb els obtinguts experimentalment per IXS. S'infereix que el potencial EAM augmenta la interacció entre modes longitudinals i l'excés de modes del BP. Finalment s'obtingué la fragilitat en els sistemes estudiats mitjançant el càlcul de la viscositat a temperatures diferents. És conegut experimentalment que la fragilitat augmenta amb la velocitat de refredament. Els sistemes LJ mostraren una fragilitat molt més alta que els Morse i EAM. No obstant això, fins i tot els sistemes simulats amb potencials realistes van mostrar valors de la fragilitat molt superiors als obtinguts experimentalment a causa de l'extrema velocitat extrema de refredament de les simulacions El desarrollo de nuevos materiales tiene impacto en todas las áreas de la ingeniería, y en particular en la ingeniería aeronáutica. Los vidrios metálicos son materiales relativamente nuevos, con excelentes propiedades mecánicas; su estudio es imprescindible para su implantación tecnológica. Las propiedades mecánicas macroscópicas de un material están determinadas por su estructura atómica. En particular, la fractura de materiales frágiles se inicia mediante la generación de modos de vibración. En los vidrios metálicos, con estructura amorfa, el espectro vibracional tiene características específicas. En este trabajo es estudian las propiedades vibracionales de los vidrios metálicos usando simulaciones de Dinámica Molecular. Se estudian sistemas binarios utilizando potenciales atómicos de Lennard-Jones (LJ), Morse y Embedded atom method (EAM), de tipo semiempírico. Al igual que en los vidrios metálicos a base de Pd, la relación de las masas de ambas especies en las simulaciones es alta, siendo 2 en potenciales LJ y 1,67 en potenciales Morse y EAM. Las simulaciones a gran escala permiten simular sistemas con heterogeneidades a escala nm, y la simulación a diferente velocidad de enfriamiento permite obtener configuraciones en diferentes estados de relajación. La dinámica de las vibraciones atómicas de los vidrios metálicos es un tema de debate. El origen del exceso de los modos de vibración conocidos como Boson Peak (BP) no es claro. En los sistemas analizados se observa que la dependencia de la posición y la intensitat del BP con el tamaño del sistema es débil. Por el contrario, la intensidad del BP aumenta con la velocidad de enfriamiento, mientras que su posición se desplaza a frecuencias menores. Los resultados obtenidos mediante el uso de potenciales realistas tipo EAM coinciden con los datos experimentales disponibles en vidres de composiciones similares. El factor de estructura dinámica, S (q, ω) se calculó también en sistemas grandes para obtener información sobre el comportamiento de las excitaciones acústicas en vectores de onda bajos. También se obtuvo la relación de dispersión de fonones longitudinal read less

Abstract: Carrying out molecular dynamics (MD) simulations is a relevant way to understand growth phenomena at the atomic scale. Initial conditions are defined for reproducing deposition conditions of plasma sputtering experiments. Two case studies are developed to highlight the implementation of MD simulations in the context of plasma sputtering deposition: ZrxCu1−x metallic glass and AlCoCrCuFeNi high entropy alloy thin films deposited onto silicon. Effects of depositing atom kinetic energies and atomic composition are studied in order to predict the evolution of morphologies and atomic structure of MD grown thin films. Experimental and simulated x-ray diffraction patterns are compared. read less

Abstract: A numerical study, within the framework of molecular statics, is conducted to assess the effect of a fixed and migrating hydrogen atom on the stress–strain data and the topological changes taking place in a 3D BCC α-iron crystal subjected to a tensile elongation. A pair-wise Morse potential is used to describe the interatomic forces. The results for a crystal with 2324 iron atoms show that the presence of a hydrogen atom, either migrating or fixed, produces relatively small effect on the stress–strain data within the elastic and some plastic range of loading. However, the topological changes, represented by the changes in the nearest neighbors for each atom within the cut-off distance after each displacement increment, are substantially different. Similarly, a comparison of the changes in the atomic potential energies when the sudden drop in stresses takes place shows differences between the two cases. read less

Abstract: A molecular dynamics simulation considered of chip deformation and force analysis for grinding process of Mg-Al alloy is presented. Hybrid potentials including embedded atom method (EAM) potential and Morse potential are applied in this model. The activities among atoms of Mg-Al Alloy material is described by EAM potential which is very suitable for metal materials. Morse potential is used to realize the interaction between Mg-Al alloy and abrasive grain made of diamond. Simulations of Different depths of cut (0.6nm, 0.8nm and 1.0nm) and different cut speeds (50m/s, 100m/s and 200m/s) are given. The experience result shows that with the same nanometric depth of cut, there is a little difference of ratio of the cut potential to the cutting speed. Moreover, with the same cutting speed, the cut potential is increased linearly with the depth of cut while reaching to stable cutting regime. read less

Abstract: Abstract. An orthogonal cutting is a symmetric cutting thus it can be modified as a two dimensional cutting. This paper uses quasi-steady molecular statics method to carry out simulation of two dimensional nanoscale cutting copper work piece by the diamond tools. For the two dimensional quasi-steady molecular statics nanoscale cutting model used by this paper, when the cutting tool moves on a copper work piece, displacement of atoms is caused due to the effects of potential on each other. After a small distance that each atom moves is directly solved by the calculated trajectory of each atom, the concept of force balance is used. The minimum energy method is employed to carry out the search, and obtain the new movement position for each atom. Based on the simulation results, this paper studies the chip formation shape and cutting forces in x direction and y direction. read less

Abstract: This study focuses on the microscopic modeling of 0-25 keV Bi 1-3-5 and C60 cluster impacts on three different targets (Au crystal, adsorbed Au nanoparticle, and organic solid), using molecular dynamics simulations, and on the comparison of the calculated quantities with recent experimental results, reported in the literature or obtained in our laboratory. The sputtering statistics are reported, showing nonlinearity of the sputtering yields with the number of cluster atoms at the same incident velocity for Bi1-5 bombardment. They are compared to experiments (especially for the organic target), and the microscopic explanation of the observations is analyzed. The results show that the respective behaviors and performances of the different projectiles are strongly dependent on the target, with clusters of heavy Bi atoms being more efficient at sputtering gold and, conversely, fullerene clusters inducing the largest sputtering yields of the organic material (mass matching). For organic targets, some important and novel conclusions of this work are the following: (i) The increase of the sputtering yield when going from Bi atoms to Bi clusters is insufficient to explain the much larger increase of characteristic ion yields, suggesting a projectile-dependent ionization probability. (ii) The extent of molecular fragmentation follows the order of Bi > Bi3 > Bi5 > C60, that is, softer emission with larger clusters. (iii) Even 5-10 keV Bi atoms create collective molecular motions and craters in the polymeric solid, though the collision cascades are rather dilute. Finally, a second series of simulations performed at low energies predict that 0.1-1 keV Bin clusters should not provide better results for sputtering and depth profiling than isoenergetic single atoms. © 2013 American Chemical Society. read less

Abstract: The effect of interatomic potentials on the onset of plastic deformation in the nanometric machining of a crystalline diamond tool on a crystalline copper workpiece, was investigated by using the MD simulation. Three potential pairs were used for the copper-copper (workpiece) and the copper-carbon (tool-workpiece interface) atomic interactions. For case 1, the Morse potential was used for both the copper-copper and the copper-carbon interactions; for case 2, the Embedded Atom Method (EAM) potential was used for the copper-copper interactions and the Morse potential was used for the copper-carbon interactions; and for case 3, the EAM potential was used for the copper-copper interactions and the Lennard-Jones (LJ) potential was used for the copper-carbon interactions. The diamond tool was modelled as a deformable body and the Tersoff potential was applied for the carbon-carbon interactions. From the simulation results, pile-up volume and the force ratio appear to indicate the onset of plasticity during the machining. The pile-up volume shows that ploughing starts from 0.25nm, 0.20 and 0.30nm depth of cut for case 1, case 2 and case 3 respectively and the formation of chips starts to occur from the depth of cut of 1.5nm for case 3. The force ratio also indicate the onset of ploughing at different depths of cut from 0.10nm-0.3nm. read less

Abstract: Improving machined surface integrity is one of the important issues in the precision machining. This study aims to develop a cutting tool, which enables to generate a local hydrostatic pressure field in the vicinity of the cutting point to suppress the extra plastic flow in the workpiece, because it is known that materials including metals never cause plastic flow and fracture no matter how much greater hydrostatic pressure field is given. In this paper, a simple cutting tool with planer jig is proposed and a molecular dynamics simulation of cutting is performed as the first step. As a result, it is confirmed that the reduction of the plastic deformation, mainly in the burr formation become remarkable with the proposed model due to the suppression of extra side plastic flow, and relatively high-hydrostatic stress field is formed in the vicinity of cutting point. However, it is also observed that relatively many dislocations are generated beneath the cutting groove. read less

Abstract: The three-dimensional quasi-steady molecular statics nanocutting model developed by this paper carries out simulation analysis of nanocutting of sapphire substrate in order to explore the effects of tools with the same tip radii of probe and straight-line cutting at different cutting depths, on cutting force. The three-dimensional quasi-steady molecular statics nanocutting sapphire workpiece model first assumes the trajectory of each atom of the sapphire workpiecs being cut whenever the diamond cutter goes forward one step. It then uses the optimization search method to solve the force equilibrium equation of the Morse force in the X, Y and Z directions when each atom moves a small distance, so as to find the new movement position of each atom, and step by step calculates the behavior during cutting. And from the simulation results of cutting force, down force and side force, it is found that under the actions of cutting tools with the same tip radius of probe, cutting force enlarges with the increase of cutting depth. This result is identical to the actual experimental phenomena of nanocutting. From this, it is known that the simulation model developed in this study is reasonable. read less

Abstract: This paper uses quasi-steady molecular statics method to carry out simulation of nanoscale orthogonal cutting of single-crystal copper workpiece by the diamond tools with different edge shapes. Based on the simulation results, this paper analyzes the cutting force, equivalent stress and strain, and temperature field. For the three-dimensional quasi-steady molecular statics nanocutting model used by this paper, when the cutting tool moves on a workpiece, displacement of atoms is caused due to the effects of potential on each other. After a small distance that each atom moves is directly solved by the calculated trajectory of each atom, the concept of force balance is used. And Hooke-Jeeves direct search method is also used to solve the force balance equation, and obtain the new movement position. When chip formation and the size of cutting force during cutting are calculated, further analysis is made. After the position of an atom’s deformation displacement is acquired, the shape function concept of finite element is employed to obtain the atomic-level equivalent strain. With the stress-strain curve obtained from experiment of the numerical tensile value of nanoscale copper film taken as the foundation, regression treatment is made, and then the flow stress-strain relational equation is acquired. The flow stress-strain curve is used to calculate the equivalent stress produced under equivalent strain of element. This paper further supposes that workpiece temperature is mainly produced from two heat sources: plastic deformation heat and friction heat. Thus, this paper uses the acquired equivalent stress and strain to calculate plastic deformation heat. Besides, this paper additionally develops a method to calculate the numerical value of friction heat produced by the workpiece atoms on the tool face and the numerical value of temperature rise of workpiece atoms on tool face. Finally, the temperature rise produced from the two heat sources is added up for calculation of temperature field of the cut single-crystal copper workpiece during nanoscale orthogonal cutting, and for making analysis. 1 Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan. 144 Copyright © 2012 Tech Science Press CMC, vol.27, no.2, pp.143-178, 2012 read less

Abstract: Great prospect in ultra precision leads to the urgent requirement for the research on the nanometric machining of metallic glass (MG). Molecular dynamics simulation is carried out to find out the nanometric cutting mechanisms of MG. The MG workpiece, Cu50Zr50, is prepared using fast cooling simulation in isothermal-isobaric ensemble. Interactions of Cu and Zr atoms are described by Finnis-Sinclair potential. Morse potential is adopted for the interaction between the carbon atom in the diamond tool and the metal atom in the workpiece. Simulation results show that, different from cutting crystal material, there is not visible shear zone ahead of the tool. That is to say the mechanism in nanometric cutting MG may be plastic cutting. read less

Abstract: The three-dimensional quasi-steady molecular statics nanocutting model is used by this paper to carry out simulation analysis of nanocutting of sapphire in order to explore the effects of conical tools with different tip radii of probe and straight-line cutting at different cutting depths, on cutting force. Meanwhile, this paper uses a cutting tool of atomic force microscopy (AFM) with a probe tip similar to a semisphere to conduct nanocutting experiment of sapphire substrate. Furthermore, from the experimental results of nanocutting sapphire substrate, this paper innovatively proposes the theoretical model and equation that the specific down force energy (SDFE) during nanocutting by using AFM probe as the nanocutting tool, is approximately a constant value. This paper uses three-dimensional quasi-steady molecular statics nanocutting model to simulate calculation and obtain nanocutting down force. It is compared with the down force calculated by SDFE theoretical equation proposed for verification. As a result, the down force obtained by the paper’s simulation is very close to the down force calculated by SDFE theory. Therefore, it can be verify that the three-dimensional quasi-steady molecular statics nanocutting theoretical model used by this paper is feasible. The SDFE proposed by this paper is defined as equating to down force energy dividing the removed volume of down press of the workpiece by the AFM probe. From the experimental data and the calculation results, it is found that the values of SDFE under different down force actions are almost close to a constant value. The three-dimensional quasi-steady molecular statics nanocutting sapphire workpiece model is to find the trajectory of each atom of the sapphire workpiecs being cut whenever the diamond cutter goes forward one step. It uses the optimization search method to solve the force equilibrium equation of the Morse force in the X, Y and Z directions when each atom moves a small distance, so as to find the new movement position of each atom, and step by step calculates the behavior during cutting. 1 Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan. 76 Copyright © 2011 Tech Science Press CMC, vol.25, no.1, pp.75-106, 2011 read less

Abstract: This article presents a quasi-steady molecular statics nanocutting simulation model for simulating orthogonal two dimension cutting copper materials with different point defects by using diamond cutters. The analyses of cutting action, cutting force, equivalent strain and equivalent stress are taken during nanocutting copper material with point defect. The two dimensional quasisteady molecular statics nanocutting model first assumes the trajectory of each atom of copper workpiece being cut whenever the diamond cutter goes forward one step. It then uses the Hooke- Jeeves search method to solve the force equilibrium equation of the Morse force in X and Y directions when each copper atom moves a small distance, so as to find the new movement position of each copper atom. Then, the displacement of the acquired new position of each atom combined with the concept of shape function of finite element method are employed to calculate the equivalent strain of the copper workpiece during nanocutting . By using the relationship equation of the flow stress-strain curve, the equivalent stress of the copper workpiece during cutting can also be calculated read less

Abstract: The paper uses three‐dimensional quasi‐steady molecular statics nanocutting model to perform simulative cutting of single‐crystal silicon. The study is different from the past literature that those papers mostly used molecular dynamics (MD) to perform simulation of nanocutting. Regarding the simulated cutting of single‐crystal silicon performed by the paper by using the nanoscale cutting model of three‐dimensional quasi‐steady nanoscale molecular statics method, it is a concept that the method of calculating the movement track of each atom is used to directly acquire the applied equilibrium force when each atom moves for a small distance. The paper uses optimized method to solve the equation of equilibrium force, find out the new movement position, and step by step calculate the cutting behavior in times of cutting. In order to prove the feasibility of the paper’s use of three‐dimensional quasi‐steady molecular statics nanoscale cutting model of single‐crystal silicon, the paper simulates a diamond cuttin... read less

Abstract: This study aims to clarify the friction and wear phenomena, which are of great importance in abrasive machining with atomic-scale material removal, such as polishing of magnetic disk substrates and CMP of semiconductor substrates. Various phenomena that occurred when a well-defined copper surface rubbed by an extremely fine rigid diamond abrasive, such asthe sliding without removal and the atomic-scale wear, were analyzed using a molecular dynamics model, in which the abrasive grain was connected to a three-dimensional spring and the holding rigidity of the abrasive grain was taken into account. A series of simulations using different indentation depths clarified that the one- or two-dimensional atomic-scale stick-slip phenomenon in proportion to the period of atomic arrays of workpiece surface occurred in the sliding processes without atomic removal. The results also demonstrated that the period and amplitude of the fundamental stick-slip wave varied when accompanied with atomic removal due to the increase in normal load. read less

Abstract: The paper develops a quasi-steady molecular statics model to analyze nanoscale cutting of copper materials by diamond cutters with different shapes. Cutting action, cutting force, equivalent strain and equivalent stress are discussed and compared. The quasi-steady molecular statics nanocutting model first assumes the trajectory of each atom of the copper workpiece being cut whenever the diamond cutter goes forward one step. It then uses the optimization search method to solve the force equilibrium equation of the Morse force in the X and Y directions when each atom moves a small distance, so as to find the new movement position of each atom. Since the force equilibrium equation of the model has two unknowns to be solved, i.e. the x and y coordinates for each position, a method in engineering optimization can be used to find the new movement position of each atom when the force equilibrium equation is satisfied. After that, the displacement of the acquired new position of each atom combined with the concept of shape function of finite element method are employed to calculate the equivalent strain of the copper workpiece during nano-cutting. By using the relationship equation of the flow stress-strain curve, the equivalent stress of the copper workpiece during nano-cutting can be obtained. The cutting forces of nanoscale cutting for a copper workpiece acquired in this paper are compared with previous results to verify that the model developed by this paper is reasonable. read less

Abstract: Based on the molecular mechanics, this study uses the two-body potential energy function to construct a trapezoidal cantilever nano-scale simulation measurement model of contact mode atomic force microscopy (AFM) under the constant force mode to simulate the measurement the nano-scale V-grooved standard sample. We investigate the error of offset distance of the cross-section profile when using the probes with different trapezoidal cantilever probe tip radii (9.5, 8.5, and 7.5 A) to scan the peak of the V-grooved standard sample being reduced to one-tenth (1/10) of its size, and use the offset error to inversely find out the regression equation. We analyze how the tip apex as well as the profile of the tip edge oblique angle and the oblique edge angle affects the offset distance. Furthermore, a probe with a larger radius of 9.5 nm is used to simulate and measure the offset error of scan curve, and acquire the regression equation. By the conversion proportion coefficient of size (omega), and revising the size-reduced regression equation during the small size scale, a revised regression equation of a larger size scale can be acquired. The error is then reduced, further enhancing the accuracy of the AFM scanning and measurement. read less

Abstract: The phenomena of Coulomb explosion require the consideration of special relativity due to the involvement of high energy electrons or ions. It is known that laser ablation processes at high laser intensities may lead to the Coulomb explosion, and their released energy is in the regime of kEV to MeV. In contrast to conventional molecular dynamics (MD) simulations, we adopt the three-dimensional relativistic molecular dynamics (RMD) method to consider the effects of special relativity in the conventional MD simulation for charged particles in strong electromagnetic fields. Furthermore, we develop a Coulomb force scheme, combined with the Lennard-Jones potential, to calculate interactions between charged particles, and adopt a Verlet list scheme to compute the interactions between each particle. The energy transfer from the laser pulses to the solid surface is not directly simulated. Instead, we directly assign ion charges to the surface atoms that are illuminated by the laser. By introducing the Coulomb potential into the Lennard-Jones potential, we are able to mimic the laser energy being dumped into the xenon (Xe) solid, and track the motion of each Xe atom. In other words, the laser intensity is simulated by using the repulsive forces from the Coulomb potential. Both nonrelativistic and relativistic simulations are performed, and the RMD method provides more realistic results, in particular, when high-intensity laser is used. In addition, it is found that the damage depth does not increase with repeated laser ablation when the pulse frequency is comparable to the duration of the pulse. Furthermore, we report the time evolution of energy propagation in space in the laser ablation process. The temporal-spatial distribution of energy indirectly indicates the temperature evolution on the surface of the Xe solid under intense laser illumination. read less

Abstract: Anharmonic effective potential, Extended X-ray Absorption Fine Structure (EXAFS) and its parameters of hcp crystals have been theoretically and experimentally studied. Analytical expressions for the anharmonic effective potential, effective local force constant, three first cumulants, a novel anharmonic factor, thermal expansion coefficient and anhamonic contributions to EXAFS amplitude and phase have been derived. This anharmonic theory is applied to analyze the EXAFS of Zn and Cd at 77 K and 300 K, measured at HASYLAB (DESY, Germany). Numerical results are found to be in good agreement with experiment, where unnegligible anharmonic effects have been shown in the considered theoretical and experimental quantities. read less

Abstract: We model interface formation by metal deposition on the conjugated polymer poly-para-phenylene vinylene, studying direct aluminum and layered aluminum-calcium structures Al/PPV and Al/Ca/PPV. To do that we use classical molecular dynamics simulations, checked by ab initio density-functional theory calculations, for selected relevant configurations. We find that Al not only migrates easily into the film, with a strong charge transfer to the neighboring chains, but also promotes rearrangement of the polymer in the interfacial region to the hexagonal structure. On the other hand, our results indicate that a thin Ca layer is sufficient to protect the film and maintain a well-defined metal/polymer interface, and that also a thin Al capping layer may protect the whole from environmental degradation. read less

Abstract: This paper intends to address an approach of Molecular Dynamics (MD) simulation to clarify the material deformation and removal mechanism between an abrasive grain and workpiece. The workpiece and the abrasive grain are assumed to consist of mono-crystalline copper and rigid diamond, respectively. In the present simulation model, influence of the stiffness of grinding wheel or polishing pad is taken into consideration. From the simulation results, relationships between material removal process and dynamics of the slip deformation, influence of the grinding wheel stiffness on the chip formation process and the actual depth of cut and so on, are clarified. These results indicate that the MD simulation has an advantage in deciding the stiffness of the tools and in estimating the actual depth of cut. read less

Abstract: This study constructs a contact-mode atomic force microscopy (AFM) simulation measurement model with constant force mode to simulate and analyze the outline scanning measurement by AFM. The simulation method is that when the probe passes the surface of sample, the action force of the atom of sample received by the atom of the probe can be calculated by using Morse potential. Through calculation, the equivalent force on the cantilever of probe can be acquired. By using the deflection angle equation for the cantilever of probe developed and inferred by this study, the deflection angle of receiving action force can be calculated. On the measurement point, as the deflection angle reaches a fixed deflection angle, the scan height of this simulation model can be acquired. By scanning in the right order, the scan curve of the simulation model can be obtained. By using this simulation measurement model, this study simulates and analyzes the scanning of atomic-scale surface outline. Meanwhile, focusing on the tip radii of different probes, the concept of sensitivity analysis is employed to investigate the effects of the tip radius of probe on the atomic-scale surface outline. As a result, it is found from the simulation on the atomic-scale surface that within the simulation scope of this study, when the tip radius of probe is greater than 12 nm, the effects of single atom on the scan curve of AFM can be better decreased or eliminated. read less

Abstract: We investigate the dependence of the hardness of materials on their elastic stiffness. This is possible by constructing a series of model potentials of Morse type; starting with modelling natural Cu, the model potentials exhibit an increased elastic modulus, while keeping all other potential parameters (lattice constant, bond energy) unchanged. Using molecular-dynamics simulation, we perform nanoindentation experiments on these model crystals. We find that the crystal hardness scales with the elastic stiffness. Also the load drop, which is experienced when plasticity sets in, increases in proportion to the elastic stiffness, while the yield point, i.e. the indentation at which plasticity sets in, is independent of the elastic stiffness. read less

Abstract: This paper investigates the strain and stress distributions in a nano-scale copper thin sheet under the biaxial tensile action, within the range of elasticity, by employing the molecular dynamics (MD) and finite-element method (FEM). Each atom is regarded as a node and the lattice as an element. The nano-scale copper thin sheet model, established in this study, is based on the face centered cubic lattice structure, and divides the lattice into 24 constant strain tetrahedron elements. After MD simulation, the biaxial force is found to be almost the same during the biaxial tensile action. Simulation results reveal that the stress and strain are highly closer at the edge of the sheet. The presence of strain around the upper and lower surfaces in the central region of the thin sheet indicates that after exhibiting biaxial tensile activity, contraction occurs in the region. The FEM/MD model, constructed in this paper directly melts the FEM spirit in MD computation. This facilitates the analysis of stress and strain in the entire nano-scale range for the nano-scale copper thin sheet. read less

Abstract: The motion of both Lennard-Jones solids and metals induced by ultrashort laser irradiation near the ablation threshold is investigated by molecular dynamics simulation. The universality of the ablation threshold fluence with respect to the cohesion energy of solids irradiated by femtosecond laser pulses is demonstrated for Lennard-Jones solid and metals simulated by many-body EAM potentials. read less

Abstract: Atomistic simulations using molecular dynamics (MD) method are conducted to check the conditions of the onset of fracture at the interface edges with a variety of angles. The simulations are facilitated with model bi-material systems interacting with Morse pair potentials. Three simulation models are considered, i.e. the interface edges with angles 45°, 90° and 135°, respectively. The simulation results show that, at the instant of crack initiation, the maximum stresses along the interfaces reach the ideal strength of the interface; also, the interface energies just decrease to below the value of the intrinsic cohesive energy of the interface. And the onset of fracture at the interface edges with different geometries is controlled by the maximum stresses or the cohesive interfacial energy. read less

Abstract: Molecular dynamics (MD) simulations are performed to study the onset of fracture at the free edges of bi-material interfaces. The objective is to see whether a unified criterion could be formulated for crack initiation at interface edges with different angles or not. The simulations are facilitated with model bi-material systems interacting with Morse pair potentials. Three simulation models are considered, i.e. the interface edges with angles 45°, 90° and 135°, respectively. The simulation results show that, at the instant of crack initiation, the maximum stresses along the interfaces reach the ideal strength of the interface; also, the interface energies just decrease to below the value of the intrinsic cohesive energy of the interface. These findings revealed that the onset of fracture at the interface edges with different geometries could be controlled by the maximum stresses or the cohesive interfacial energy. read less

Abstract: This study aims to clarify the interaction between Si wafer and individual diamond abrasives in grinding at nanometer level and to estimate the grinding conditions for minimizing the surface defect. This paper reports on the results obtained through nano-scratching experiments in vacuum by an atomic force microscope (AFM) and simulations by using the molecular dynamics method by applying Tersoff potential for Si-Si atomic interaction under room and high temperature, respectively, to examine the influence of the grinding heat on the materials removal process. As a result, it was proven that the scratch groove under high temperature becomes deeper than that under room temperature from the experiments, and it was also observed that the formation of the amorphous phase around the scratch groove under high temperature becomes a little bit larger than that under room temperature from the simulations. read less

Abstract: This study aims to clarify the effectiveness of the mechanism of application of vibration on the reduction of plastic flow and improvement of machined surface in the micro/nano cutting for three-dimensionally shaped microparts. The molecular dynamics method has been applied to analyse the vibration-assisted cutting. In the simulations, the cutting tool and the workpiece are assumed to be rigid diamond and pure aluminium, respectively. This paper reports the results examined on the effect of the vibration, acceleration and velocity on the reduction of plastic flow and cutting forces. As a result, it was understood that the effect of the vibration on the reduction of both the plastic flow and cutting forces is very much significant compared to that due to acceleration and velocity. read less

Abstract: This study aims to clarify the effectiveness and the mechanism of the application of vibration on the reduction of plastic flow and the improvement of machined surface in the micro/nano cutting for three-dimensionally shaped micro-parts. The molecular dynamics method has been applied to the analysis of extremely small amplitude and high-frequency vibration-assisted cutting processes. In the simulations, the cutting tool and the workpiece are assumed to be rigid diamond and pure aluminium, respectively. In this paper, the effect of the vibration parameters, such as frequency and amplitude on the reduction of plastic flow and cutting forces, was mainly examined and clarified. As a natural result, necessitated vibration parameters for the improvement in the machined surface quality were also obtained. read less

Abstract: The nanoimprinting process between a nickel mold and a gold thin film consisting of 9500 – 11000 atoms was studied using molecular dynamics computational simulation. The nickel mold and the gold thin film were both formed in face central cubical (FCC) single crystal, and the simulation condition was in an isothermal state of 300K. The Morse potential was utilized in order to determine interatomic forces and potentials. During the nanoimprinting process, jump-to-contact, thin-film recovery, slip-line like, dead-metal zone and dislocation phenomena were observed. After finishing nanoimprinting processes, the interactive force curves between the mold pattern and thin film, and those inside the thin film were measured. By varying the pattern width of the mold and incorporating the measured force curves inside the thin film, the length effect on metallic pattern formation can be determined. In addition, through analytical investigation, it can be observed that the thin-film thickness, the pattern width of the mold, and the applied force should be matched up very well in order to obtain good formation of metallic pattern. read less

Abstract: Large-scale non-equilibrium molecular dynamics simulations are used to investigate the ejection of the metal under a shock loading. The present work focus on the dynamic process of ejection from the metal Cu and Al surface groove under shock loading, using parallel MD implementation and the Morse potential. The ejected mass coefficient and the size distribution of ejected particles (cluster for atoms) are investigated with changes of the half-angle or the depth of groove and shock strength. read less

Abstract: We describe the experimental and molecular dynamics simulation study of crystalline copper (Cu) ablation using femtosecond lasers. This study is focused on the heat-affected zone after femtosecond laser ablation and the laser ablation rate. As a result of the x-ray diffraction measurement on the ablated surface, the crystallinity of the surface is partially changed from a crystal structure into an amorphous one. At the laser fluences below the ablation threshold, the entire laser energy coupled to the Cu target is absorbed, while during the fluence regime over the threshold fluence, the ablation rate depends on the absorption coefficient, and the residual energy which is not used for the ablation, is left in the Cu substrate. The heat-affected zone at the fluences below the threshold is estimated to be greater than that over the threshold fluence. In addition, the laser ablation of Cu is theoretically investigated by a two-temperature model and molecular dynamics (MD) simulation to explain the heat-affect... read less

Abstract: In this work, Molecular Dynamics (MD) simulation is employed to investigate femtosecond laser ablation of copper, with an emphasis on the understanding of the mechanism of phase change during laser ablation. Laser induced heat transfer, melting, surface evaporation, and material ablation are studied. Theoretically, it has been suggested that under intense femtosecond laser irradiation, the material undergoes a volumetric phase change process; its maximum temperature can be close to or even above the thermodynamic critical point. The MD simulations allow us to determine the transient temperature history of the irradiated material and to reveal the exact phase change process, which explains the mechanisms of femtosecond laser ablation. A finite difference calculation is also performed, which is used to compare results of heating and melting prior to a significant amount of material being ablated. read less

Abstract: Thermal and thermomechanical phenomena in laser metal interaction are of great importance in terms of understanding the underlying mechanisms in laser materials processing, optimizing the efficiency of laser micro-machining, and minimizing laser induced damage. In this work, Molecular Dynamics (MD) simulation is carried out to investigate picosecond laser copper interaction. A method has been developed to account for the laser beam absorption in, and the thermal transport sustained by, free electrons. Superheating is observed, and an evident temperature drop is revealed at the solid-liquid interface, which moves at a speed of 4400 m/s. However, the later phase change from solid to liquid happens in the target simultaneously and no visible movement of solid-liquid interface is observed. The results show that the laser induced stress wave consists of a strong compressive stress and a weak tensile stress. After reflection at the back side of the MD domain, the strong compressive stress becomes a strong tensile stress, which results in a visible drop of the number density of atoms. In the presence of this strong tensile stress, voids have formed in the region near the back side of the MD domain, indicating that the strong tensile stress in laser materials interaction plays an important role in terms of inducing structural damage. @DOI: 10.1115/1.1725092# read less

Abstract: The stress concentration near the interface edge of a film/substrate, which dominates the delamination, is analyzed by molecular dynamics (MD) analysis. Here, the film thickness is on the nanoscale and the interatomic interaction is simulated by Morse-type model potentials. Three types of load are applied to the film/substrate to examine the effect of the stress-concentrated region on the delamination at the interface edge. At lower applied load, the stress distribution along the interface near the edge in the MD simulation coincides well with that obtained by linear elastic analysis (FEM: Finite Element Method). However, after the stress near the edge reaches the ideal strength of the interface, it deviates from the FEM result. The delamination crack is initiated from the free edge when the stress at y < 1nm (y: distance from the edge)reaches the ideal interface strength. This signifies the criterion of interface toughness that the delamination is governed by the stress in the region (process zone). This also suggests the limit of applicability of linear elastic fracture mechanics on the nanoscale components. read less

Abstract: A computationally efficient, physics-based technique is described for calculating the composition dependence of single crystal elastic constants of disordered, single-phase alloys with face-centered cubic and body-centered cubic Bravais lattices. Alloys are modeled as virtual crystals in which the energy of representative atom pairs is approximated by a virtual potential constructed from the pair potentials of component pairs using a quasi-chemical approximation. Following the method of long waves, second-order elastic constants are calculated from first and second neighbor axisymmetric force constants obtained from the virtual potential. Since only elastic constants are modeled, the form of the potential employed contains only parameters that describe the slope and curvature in the vicinity of the first and second nearest neighbors. Examples are presented for several binary alloy systems differing in solubility characteristics and crystal structures of the pure solutes. read less

Abstract: Dynamics of surface atoms penetrating into microclusters is investigated in connection with the very rapid alloying phenomenon in metal microclusters first discovered by Yasuda, Mori M. Komatsu, K. Takeda, and H. Fujita, J. Electron Microsc. 41, 267 (1992). A new algorithm to simulate the cluster dynamics where isothermal condition is satisfied without adding any stochastic noise is developed in order to suppress gradual temperature rise due to the emission of reaction heat. The dependence of radial diffusion and alloying processes on temperature and negative heat of solution are elucidated separately. The diffusion process obeys an Arrhenius-like law, and unexpectedly, the radial diffusion rate is not very sensitive to the magnitude of negative heat of solution. This fact implies that the rapid diffusion is not a peculiar feature of binary clusters but a universal feature of small clusters. However, the magnitude of negative heat of solution still dominates the alloying process through a preexponential factor. The mechanism causing the rapid radial diffusion is quite different from the mechanism of diffusion in bulk solid, and very active motion of atoms along the surface of cluster plays a crucial role. Based upon our quantitative results, the mechanism with which the surface activity is converted into the rapid radial diffusion is discussed. read less

Abstract: In the present work, several molecular dynamics simulations have been performed to clarify dynamically the contact mechanism between the specimen surface and probe tip in surface observations by an atomic force microscope (SFM) or friction force microscope (FFM). In the simulation, a three-dimensional model is proposed where the specimen and the probe are assumed to consist of monocrystalline copper and rigid diamond or a carbon atom, respectively. The effect of the cantilever stiffness of the AFM/FFM is also taken into consideration. The surface observation process is simulated on a well-defined Cu{100} surface. From the simulation results it has been verified that the surface images and the two-dimensional atomic-scale stick-slip phenomenon, just as is the case for real AFM/FFM surface observations, can be detected from the spring force acting on the cantilever. From the evaluation of the behaviour of specimen surface atoms, the importance of the specimen stiffness in deciding the cantilever properties can also be understood. The influence of the probe tip shape on the force images is also evaluated. From the results it can be verified that the behaviour of the specimen surface atoms as well as the solid surface images in AFM/FFM surface observations can be understood using the molecular dynamics simulation of the model presented. read less

Abstract: Heat transfer and phase change of an argon crystal irradiated by a picosecond pulsed laser are investigated using molecular dynamics simulations. The result reveals no clear interface when phase change occurs, but a transition region where the crystal structure and the liquid structure co-exist. Superheating is observed during the melting and vaporizing processes. The solid-liquid interface is found to move with a velocity of hundreds of meters per second, and the vapor is ejected from the surface with a vapor front velocity of hundreds of meters per second read less

Abstract: The Monte Carlo method has been applied to the study on the size dependence of mechanical properties in gold nanocontacts. Using the Metropolis method, thermal-equilibrium atomic configurations in model nanocontacts have been followed during elongation of the contacts. The Morse potential has been used as an interatomic interaction. The relation between the tensile force and strain, the change in atomic configuration during elongation, Young's modulus and the yield stress have been investigated for three different-sized nanocontacts. The simulations show that Young's modulus and the yield stress increase as the contact size increases. While the Young's modulus tends to increase gradually to the bulk value with increasing contact size, the yield stress is expected to turn decreasing with increasing size above a certain size. read less

Abstract: Numerical values are obtained for the parameters of the crystal-field potentials and crowdions (self-energy, effective mass, characteristic length) for Ar and Kr fcc cryocrystals, Cu and Al fcc metals, and α- and δ-Fe bcc metals. The calculations are performed assuming that the interatomic interaction in the crystals can be described by empirical Lenard–Jones and Morse pair potentials. A new algorithm is developed and used for calculating the crystal-field potentials. The algorithm is based on a representation of the crystal lattice as a collection of parallel atomic rows. An analytic expression in the form of a trigonometric series is obtained for the potential describing the interaction between an atom in a close-packed row and the crystal matrix. An explicit analytic expression is also obtained for the energy parameter characterizing the interatomic interaction inside a distinguished row. It is shown that the main condition for weak coupling between close-packed rows and the crystal matrix, admitting t... read less

Abstract: Nucleation and growth of fcc/bcc structural transformation are investigated in modeled crystals. To model the transformation, inter-atomic potentials are changed to initiate the transformation. During the relaxation of the fcc structure, an initial bcc structure is created in the crystals containing two dislocations. After applying bcc potential, the nucleation starts at the region where the structure is already changed before the transformation. This result suggests that the necessary condition of the nucleation site is the displacement of about two dozen atoms relevant to the bcc structure. The interaction between atoms, which reflects the fluctuation of the environmental configuration of atoms, is also necessary for the structural transformation. read less

Abstract: We have simulated the breaking process of Au nanowires using the Monte Carlo method. Nanowires for the simulation consist of atomic layers perpendicular to the [001] axis cut out from the fcc lattice. We have stretched the nanowires and have followed relaxation of atomic arrangements during elongation of the wires at 300 and 600 K. The Morse potential has been used as an interatomic potential. The simulations show that the elongation of nanowires proceeds in alternating elastic and yielding stages up to the last moment of breaking. Each elastic stage is the elongation due to an increase in interlayer spacings, and each yielding stage corresponds to an abrupt slipping event of several atoms on the {111} plane. Each slipping event causes an increase in the number of layers perpendicular to the wire axis. The nanowires break at a smaller strain at 600 K than at 300 K because of thermal atomic motions in the neck of the wire. read less

Abstract: The coefficient of restitution and the collision contact period are analyzed from a statistical-mechanical point of view through studying the collision between a one-dimensional anharmonic lattice and a rigid wall as a typical example. The contact period is defined as the time span between the first time and the last time when the atom at the end of the lattice contacts with the rigid wall. A similar collision problem for the harmonic lattice is also studied for the sake of comparison. read less

Abstract: We perform a comprehensive survey of the potential energy landscapes of 13-atom Morse clusters, and describe how they can be characterized and visualized. Our aim is to detail how the global features of the funnel-like surface change with the range of the potential, and to relate these changes to the dynamics of structural relaxation. We find that the landscape becomes rougher and less steep as the range of the potential decreases, and that relaxation paths to the global minimum become more complex. read less

Abstract: This paper describes the effect of temperature and interatomic force between a workpiece and tool on the atomic-scale cutting mechanism, by means of molecular dynamics simulation. The interatomic force between the workpiece and tool is assumed to be derived from the Morse potential function. Molecular dynamics cutting simulations were carried out using a rigid pin tool, with changing of the temperature and the value of Morse potential parameters γ0, D and α. The increase in the potential parameters D and α resulted in the positive effect of surface roughness, but the increase in the parameter γ0 and temperature resulted in the negative effect of surface roughness. Chip formation and side flow resulted due to the collision between the workpiece and tool, which lead to a temperature increase of the workpiece. The surface of workpieces observed experimentally in micro-scale cutting was similar to that in atomic-scale cutting by molecular dynamics simulation. read less

Abstract: Molecular dynamics (MD) simulations have been used to model the high energy particle bombardment process of deuteated alkanethiol chains chemisorbed on a gold surface. The model involves the use of sophisticated many-body potential energy functions to represent the chemical interactions among atoms. We have investigated the dependence of the fragmentation pattern upon two different angles of the Ar incidents, namely in the direction parallel (−35°) and orthogonal (+55°) to the tilt chain. It is found that surface thiol chains are likely to be hit for Ar at +55° so that more fragmentation occurs. In contrast, collisions with substrate atoms are more likely when Ar impacts at −35°. This leads to less fragmentation and more molecular species are sputtered. We also found that hydrocarbon fragments such as C2D5, C3D7, and C4D9 are prominent for both angles of incidence although the suggested mechanisms leading to their ejections are different. read less

Abstract: Molecular dynamics simulations of the Ni/Pd film formation process were performed by employing the embedded atom method with the high (10 eV) and low (0.1 eV) kinetic energies of incident atoms. At 10 eV, layer by layer growth with the interdiffusion of Ni and Pd atoms at the interface was observed. At 0.1 eV, an island growth mode was observed, in which Pd atoms fall onto the indented part of Ni layer, producing mixed layers of Pd and Ni atoms. The origins of the interfacial roughness are different for the cases of high and low energy of incident atoms. The dependence of the strain in Ni layers at the interface on the kinetic energy of incident atoms is in good agreement with experimental results. read less

Abstract: Reflection of nonlinear waves, which are excited by impulsive forces, in one-dimensional crystal lattices at finite temperatures, and dynamic fracture of the lattice induced by the reflection are numerically analyzed using the basic statistical-mechanical equations proposed in the preceding paper. Enhancement of the strength of the reflected waves, and typical fracture patterns are found. Their physical implications are also briefly discussed. The equations are, therefore, confirmed to be valid for analyzing such nonequilibrium phenomena. read less

Abstract: An analysis of the dynamic behaviour associated with a simple atomistic model of a crack tip is presented. The model consists of a linear array of four atoms, with nearest neighbours interacting via a Morse-function potential. Energy exchange with the surroundings is simulated by driving the two outer atoms, that is, forcing them to oscillate sinusoidally with time, and by allowing the motion of the two inner atoms to be damped. The damping may be at least qualitatively related to dissipative mechanisms that may occur at the tip of a crack. Emphasis is placed on determining conditions under which the two inner atoms, which represent the crack tip, oscillate in a chaotic or aperiodic manner in response to the driving and damping. The amplitude of tile driving oscillation and the damping constant are treated as variable parameters in this regard. As expected, chaotic behaviour is to be found associated with larger driving amplitudes and smaller damping constants. Extreme sensitivity of chaotic motions to minute changes in initial conditions is explored. The temperature associated with the two inner atoms, calculated in terms of their time-averaged kinetic energy, can undergo a large increase when the transition from periodic to chaotic oscillations takes place. In addition, the non-linear dynamics is, under some conditions, found to be characterized by hyperchaos, that is, by the existence of two positive Lyapunov exponents. Qualitative implications of the results, relative to actual fracture processes, are discussed. read less

Abstract: This paper describes a systematic microscopic study of solute segregation and ordering at a grain boundary. We develop for this inhomogeneous system several Monte Carlo techniques and apply these to analyze the distribution of substitutional impurities near a symmetric coincident‐site‐lattice tilt boundary. The calculations demonstrate the importance of ensemble and boundary condition for a Monte Carlo simulation, especially one with an inhomogeneous lattice and with ordering, as opposed to segregating, bulk interactions. The resulting concentration profiles exhibit segregation to the boundary at high temperatures and bulk ordering at low temperature. Based on our results, we propose a mechanism for a solid–solid interfacial ordering phase transition previously suggested by experiment. We also compare these simulations to our earlier one‐dimensional mean‐field work and find that the three‐dimensional simulations confirm the essential mean‐field predictions. read less

Abstract: The collisional dissociation of the H‐surface bond and the formation of the H–O2 bond in the O2(gas)/H(ads) collision taking place on a tungsten surface have been studied by classical trajectory methods over the collision energy range of 0.1–2.0 eV. The effects of the interactions between the H atom and higher‐order neighbors of the center metal atom are important in the collisional dissociation of adatoms. This many‐body interaction leads to an oscillatory dependence of the adatom dissociation probability on the collision energy. The attractive well depth of the O2(gas)/H(ads) interaction is varied between 0.202 to 4.624 eV. At an intermediate range of well depth, energy preferentially transfers into the adatom bond and leads to a large dissociation probability. As well depth increases, energy transfer to O2 becomes significant, thus causing the accumulation of a smaller amount of energy in the adatom bond, so adatom dissociation is less effective. read less

Abstract: Molecular dynamics techniques have been used to simulate atom-atom collisional scattering of 0-5.5 eV/nucleon Ti atoms in bulk Ti. The recoiling atoms to be simulated were produced by the emission of MeV gamma -rays after the thermal neutron capture reaction 48Ti(n, gamma )49Ti. The information on the collisional scattering was deduced from Doppler broadened gamma -ray lineshapes, produced in the decay of excited bound states in recoiling 49Ti. The measured gamma -ray lineshapes were simulated by combining the molecular dynamics calculation for the atomic collisions with calculations using the Monte Carlo method for the experimental conditions and decays of excited nuclear states. The dependence of the simulated gamma -ray lineshapes on the interatomic potential is demonstrated. read less

Abstract: An analytical and computational study has been made of the influence of surface impurity on the normal impact response of two identical crystal lattices. Identical monolayers of adsorbed atoms are considered to cover each host lattice. The incoming lattice is assumed to move with uniform initial speed, impacting an initially motionless lattice. A nonlinear differential‐integral equation governing the impact response of the surface impurity is derived and then solved analytically by asymptotic expansion for compressive interaction. For numerical calculations, oxygen surface impurity and a copper host lattice are considered, with surface interaction force determined from quantum‐mechanical results. Because the surface interaction force exhibits a gradual long‐range change in force with distance, surface oscillations do not occur during impact. The time required for the surface of an impacted lattice to accelerate to the classical continuum shock velocity is shown to depend on impact velocity and two paramet... read less

Abstract: We apply a recently developed combined molecular dynamics–local Langevin equation method to the simulation of the scattering of Ar by the (100) face of a face‐centered cubic solid. The kinetic energies of the Ar are chosen to be low compared to the typical energies used in sputtering. We find that even at low energies, a significant amount of surface damage is inflicted by the Ar, leading to ejection of metal atoms into the gas phase, the formation of dislocations, and the production of isolated atoms trapped on the surface. We study both the probability that such events occur and individual trajectories which display the dynamic processes through which sputtering takes place or defects are created. read less

Abstract: We describe classical-trajectory calculations of sputtering yields for Ar/sup +/-ion collisions with a Si(001) surface. The Ar/sup +/-Si and short-ranged Si-Si interaction potentials were calculated using the ab initio Hartree-Fock and configuration-interaction methods. The low-energy potential describing the silicon solid is the two- and three-body form due to Stillinger and Weber. We compare the calculated sputtering yields with experiment. The potential-energy surface strongly influences the calculated sputtering yields, and it is found that the most reasonable agreement is obtained from our potentials using the (2 x 1) Si(001) reconstructed surface rather than the bulk-terminated surface. Analysis of the kinetic energy and angular distributions of the sputtered silicon atoms and of cluster yields has provided a mechanism of ejection. read less

Abstract: The reduced second-order self-consistent phonon approximation is applied to the investigation of the dynamic and thermodynamic properties of noble metals using the Morse and Rydberg and Varshni potentials as models of nearest-neighbour central force interaction. The temperature and pressure dependence of the dynamic and thermodynamic functions of Cu, Ag, and Au in the high and low temperature limits are given and compared with experimental and other theoretical data. The behaviour of the physical quantities in the vicinity of the instability point is investigated, too. [Russian Text Ignored] read less

Abstract: A molecular dynamics simulation has been used to investigate the sensitivity of atom ejection processes from a single‐crystal target to changes in the atom‐atom potential function. Four functions, three constructed from the Gibson potentials with Anderman’s attractive well, and a fourth specifically developed for this investigation, were investigated in the Cu/Ar+ system over a range of ion energies from 1.0 to 10.0 kev with the KSE‐B ion‐atom potential. Well depths and widths also were varied. The calculations were done at normal incidence on the fcc (111) crystal orientation. Computed values were compared with experimental data where they exist. Sputtering yields, multimer yield ratios, layer yield ratios, and the ejected atom energy distribution vary systematically with the parameters of the atom‐atom potential function. Calculations also were done with the modified Moliere function. Yields and other properties fall exactly into the positions predicted from the Born‐Mayer function analysis. Simultaneou... read less

Abstract: A detailed molecular dynamics study has been performed in order to determine the factors controlling the ejection directions of adsorbate atoms due to 600 eV Ar+ ion bombardment. The specific system studied is oxygen which dissociatively adsorbs to form a c(2×2) overlayer on Ni(001). A fourfold bridge, an atop or linear and twofold bridge bond, as well as several heights of the oxygen atoms above the surface were investigated. The angular distributions are shown to be influenced by both the bonding site and the height of the oxygen adsorbate. There are distinguishing characteristics that can be ascribed to each of these three bonding sites. read less

Abstract: We have calculated the response of a model Ni(001) microcrystallite to 600 eV Ar+ ion bombardment when it is covered with 0.5 monolayer of CO. Calculations were performed using a standard molecular dynamics treatment which employs pair potentials fit to the elastic constants of the solid to evaluate Hamilton’s equations of motion. The model microcrystallite contained ∼240 atoms. The CO was adsorbed in a c(2×2) coverage in both an atop or linear bonded and a twofold bridge bonded position with a binding energy to the surface of 1.3 eV. The results showed that most of the CO molecules eject molecularly, although a few (∼10%–15%) eject dissociatively if they are hit directly with the primary ion or with other energetic solid atoms. We also found that NiCO as well as Ni2CO and Ni3CO formation probably occurs over the surface via interaction between Ni and CO species, and that the probability of NiC or NiO clusters ejected from a CO covered surface is extremely low. read less

Abstract: Using Johnson's potential of α-iron, three dense random packing (DRP) assemblies constructed by Ichikawa's method for k = 1.05, 1.2, and 1.4, are relaxed under a free boundary condition. The assembly with k = 1.2 is relaxed also by the potential obtained by Pak and Doyama and the long range oscillatory potential of liquid iron. The pair distribution function (PDF) of the relaxed model with k = 1.2 using Johnson's potential is in excellent agreement with the experimental PDF of the amorphous iron. On the other hand, the greatest packing fraction, η = 0.59, is achieved using the potential by Pak and Doyama. It is shown that the relaxation procedure using an appropriate potential is the indispensable process to construct realistic models of glassy metals. Mit Johnson's Potential fur α-Eisen werden drei statistisch dicht gepackte (DRP) Anordnungen, die mit Ichikawas Methode fur k = 1,05; 1,2 und 1,4 konstruiert wurden, unter freier Randbedingung relaxiiert. Die Anordung mit k = 1,2 wird ebenfalls mittels des von Pak und Doyama erhaltenen und des oszillatorischen langreichweitigen Potentials von flussigem Eisen relaxiiert. Die Paar-Verteilungsfunktion (PDF) des relaxiierten Modells mit k = 1,2 und dem Johnson-Potential befindet sich in ausgezeichneter Ubereinstimmung mit der experimentellen PDF von amorphem Eisen. Andererseits wird der groste Packungsanteil, η = 0,59, mit dem Potential von Pak und Doyama erhalten. Es wird gezeigt, das die Relaxationsmethode mit der Benutzung eines geeigneten Potentials der unerlasliche Prozes fur die Konstruktion realistischer Modelle glasartiger Metalle ist. read less

Abstract: The theory of elastic constants of cubic crystals, based on a non-central atomic interaction, is modified for binary alloys with a b.c.c. structure and with interaction restricted to the first and second neighbours. It is then applied to the study of the composition dependence of elastic constants of Fe—Si alloys in the concentration range 0 to 25 at% Si and compared with recent measurements. The change of the dependence above 11 at% Si is explained by a simultaneous effect of the ordering of the alloy and of the change of its electronic structure. Die Theorie der elastischen Konstanten von kubischen Kristallen, auf der Grundlage nichtzentraler interatomarer Krafte, wird fur binare Legierungen mit k.r.z. Struktur modifiziert, wobei nur die Wechselwirkung zwischen ersten und zweiten Nachbaratomen berucksichtigt wird. Die Theorie wird fur das Studium der Konzentrationsabhangigkeit der elastischen Konstanten von Fe—Si-Legierungen im Konzentrationsbereich 0 bis 25 At% Si angewendet und mit neueren Messungen verglichen. Anderung der Konzentrationsabhangigkeit der elastischen Konstanten oberhalb 11 At% Si wird durch gleichzeitige Wirkung der Legierungsordnung und der Anderung von Elektronenstruktur erklart. read less

Abstract: The formation of clusters of sputtered copper atoms from an argon‐bombarded (100) copper surface has been simulated with a computer program which includes interatomic attractive forces. Dimer formation is very common. Most commonly, dimers are formed from atoms which were next‐nearest neighbors in the crystal. Nearest‐neighbor atom clustering is rare, and dimer formation by a single atom moving in a channel has not been observed, and could not be forced by artificial means. All multimer formation mechanisms depend strongly upon both the relatively low speed of the sputtered atoms and the relatively high speed of the knock‐on atoms involved in the sputtering mechanisms. Strong evidence for trimer formation exists. Pairs of dimers with a common atom have been observed. No quadrimers have been identified, but structures which almost meet the stability criteria have been observed. read less

Abstract: The six third-order elastic constants of single crystal ferromagnetic nickel at 80°K were determined by measurement of ultrasonic wave velocities as a function of an applied uniaxial stress. The effect of magnetic domains on the ultrasonic propagation were eliminated by keeping the specimen in a transverse saturation magnetic field. Theoretically predicted constants based on central force model are discussed with experimentally measured constants. Die sechs elastischen Konstanten dritter Ordnung von ferromagnetischen Nickeleinkristallen wurden bei 80°K durch Messung der Ultraschallgesch windigkeit in Abhangigkeit von einer auseren uniachsialen Spannung bestimmt. Der Einflus magnetischer Domanen auf die Ultraschallausbreitung wurde dadurch eliminiert, das sich die Probe in einem transversalen Sattigungsfeld befindet. Theoretisch vorhergesagte Konstanten, die auf einem Zentralkraftmodell basieren, werden mit experimentell gemessenen Konstanten diskutiert. read less

Abstract: The thermal expansion coefficient α of Fe-Ni ( fcc ) alloys was measured in the range from 800°C to room temperature. Below the Curie temperature T c , the α– T curve exhibits an anomaly corresponding to the spontaneous volume magnetostriction ω s . The `paramagnetic' thermal expansion coefficient α p below T c was determined by the extrapolation of the α– T curve above T c and the value of ω s was estimated from the difference between α p and α below T c . The relation between ω s and the change of T c with pressure was discussed. The α p vs. composition curve at a fixed temperature shows a minimum around the invar alloys. This minimum corresponds to the anomaly in the elastic moduli vs. composition curves. It is thus pointed out that the lattice energy must be considered in addition to the magnetic energy in discussing the origin of the invar properties. read less

Abstract: A study of the possibility of the existence of stacking faults in b.c.c. crystals on {110} and {112} planes has been performed, representing the lattice by a central force interaction between atoms. The same study was also carried out for {111} planes in f.c.c. crystals. The results for the f.c.c. lattice are in full agreement with the predictions based on a hard-sphere model. However, the results for the b.c.c. lattice are very different and suggest that no stable instrinsic stacking faults of the same type as in f.c.c. crystals can exist either on {110} or on {112} planes in b.c.c. crystals. read less

Abstract: 2014 Self-diffusion of gold, copper and aluminium has been investigated for single crystals treated under pressures of 0 to 10 kbars in a temperature range of 700 °C to 990 °C for copper and gold and 400-610 °C for aluminium. The influence of pressure on the coefficients and activation énergies for self-diffusion in these metals has been measured. The activation volumes obtained : 0.91 molar volume for copper, 0.72 for gold and 1.29 for aluminium are in good agreement with theory. LE JOURNAL DE PHYSIQUE TOME 29, AVRIL 1968, read less

Abstract: The binding energy of individual tungsten atoms on different planes of a tungsten crystal, heretofore inaccessible to measurement, has been explored by field desorption at 20°K. Tunneling, rather than evaporation over a Schottky saddle, is the limiting step under these conditions. The appropriate relations between desorption field and atomic binding are derived and tested by establishing the evaporation field for tungsten at 6.1 V / A. Desorption measurements on single adatoms lead to the following binding energies: (110), 5.3 eV; (211), 7.0; (310), 6.7; (111), 6.0; (321), 6.7; (411), 6.2. On low index planes such as (110), (211), and (310), agreement with the energetics estimated from Morse and Lennard‐Jones potentials is reasonable. For rougher surfaces, however, the experimental quantities are significantly smaller than expected, suggesting a fundamental limitation on such potentials. Comparison of binding energies with activation energies for diffusion over the (211) and (321) planes also leads to the... read less

Abstract: The energy changes resulting from dislocation reactions between (α/2)〈111〉{110} dislocations in body-centred cubic structures are calculated using isotropic elasticity. It is shown that when the reactants have longrange attractive forces, they should combine to form a pair of (α/2)〈100〉 dislocations which may dissociate on {110} or {100} planes, depending on the crystallography of the reaction. If the (α/2)〈100〉 pair lies in a 〈111〉 direction, an (α/6)〈111〉 twinning partial and an (α/6)〈211〉 sessile dislocation may be formed by decomposition of one of the (α/2)〈100〉 dislocations under stress. If the reactants have long-range repulsive forces, they may be forced to react under high local stress concentrations or when moving at high velocities. Stable products of such reactions are pairs of (α/2)〈110〉 dislocations extended on {110} or {100} planes. If one of the reactants is a screw, a twinning partial, (α/3)〈111〉, and an (α/3)〈221〉 sessile dislocation may be formed instead of the (α/2)〈110〉 pair. ... read less

Abstract: Elastic constants of binary alloys, Ni-Fe and Ni-Cu, of their wide composition ranges having f.c.c. structure, were measured by means of a composite oscillator method in the frequency range from 1 to 5 Mc/s at room temperature. Elastic constants of Ni-Fe alloys vary quadratically as their compositions, while those of Ni-Cu vary linearly. These results can be interpreted in terms of the central and pair-like interactions between atoms of the alloys. read less

Abstract: − In this study, we investigated the effect of the spring constant on frictional behavior at a nanoscale through molecular dynamics simulation. A small cube-shaped tip was modeled and placed on a flat substrate. We did not apply the normal force to the tip but applied adhesive force between the tip and the substrate. The tip was horizontally pulled by a virtual spring to generate relative motion against the substrate. The controlled spring constant of the virtual spring ranged from 0.3 to 70 N/m to reveal its effect on frictional behavior. During the sliding simulation, we monitored the frictional force and the position of the tip. As the spring constant decreased from 70 to 0.3 N/m, the frictional force increased from 0.1 to 0.25 nN. A logarithmic relationship between the frictional force and spring constant was established. The stick–slip instability and potential energy slope increased with a decreasing spring constant. Based on the results, an increase in the spring constant reduces the probability of trapping in the local minima on the potential energy surface. Thus, the energy loss of escaping the potential well is minimized as the spring constant increases. read less

Abstract: In order to manufacture parts with dimensions of nanometres, high–technology equipment is required. There is a demand to study nano-metric cutting mechanisms and phenomena appearing in this level. However, experiments are difficult to be realized, so computational methods are employed. Nano-scale cutting involves workpiece deformation in only a few atomic layers from the workpiece surface; at this scale the continuum theory cannot be used, so methods like finite elements are not sufficient. Molecular Dynamics is a method increasingly used for the simulation of nano-cutting. However, the computational cost required is quite high. In an effort to reduce the time of the analysis, high or extremely high cutting speeds are used in the models. In this paper an analysis is presented where cutting speed is studied and its influence on the chip morphology and workpiece surface is investigated, for nano-cutting modelling of Cu with diamond tools. The results indicate that cutting speed influences the outcome of the analysis and more attention should be paid to the selection of this parameter. read less

Abstract: Microscopic contact angle at a contact line traveling over each backward-facing step with heights of 0.3-1.2 nm was investigated with molecular dynamics (MD). The simulations were performed for a Couette-flow-like geometry which is composed of an upper flat plate and a lower plate with a step. Two kinds of immiscible liquids between the plates were sheared by the lower plate moving with a velocity of 1 m/s. When the contact line reaches the backward-facing step, it tends to be strongly captured (pinned) at the top edge of the step. The minimum contact angle of the receding fluid, which was observed at the moment of the depinning of the contact line, is decreased with the increment in the step height. In order to elucidate the mechanism relating the minimum contact angle to the step height, a description on the stress balance along the step surface was derived under the assumption of the static condition. It has been found that the static contact angle is decreased by the stress on the vertical surface of the step, the stress which associates with the anisotropic pressure in the liquid-liquid interface region. In addition, such decrement in the contact angle is enhanced by the increase in the step height through the intensification of the total shear stress over the vertical surface of the step. read less

Abstract: Molecular dynamics simulation has been performed to study the mechanical properties and behaviour of the interface between Al and Al- terminated α-Al2O3 under tension loading. The atomistic structures of the metal/ceramic interface are first modelled according to experimental results. The interatomic potential utilised here is a multicomponent potential proposed by us. The results reveal that atomic rearrangement caused by lattice misfit occurs after relaxation, expressed as the stacking-fault islands at the interface, which shows reasonable agreement with experiments. During the tension process, the system reaches its ultimate strength 7.89 GPa at strain 11.08% when the crack nucleation emerges in the aluminium. read less

Abstract: A molecular dynamics simulation is carried out to study the fractureunder hyper-velocity impact conditions when a space debris attack to aman-made satellite. In this paper, oblique-impact simulations areperformed since most orbital debris impacts are oblique in the realcondition. Aluminum projectile impacts aluminum target at 0−, 30−, and 45−degrees obliquity. Impact velocity is 8km/s, and target thickness-projectile diameter ratio t/D is 0.684. As the angle of obliquity isincreasing, the velocity of debris after impact is decreasing, whilethe deviation of the line of flight is increasing. These resultsqualitatively agrees well with experimental results. read less

Abstract: We propose a multiscale model for what consists of ab initio calculation, molecular dynamics simulation and a quasicontinuum model. First, we develop the interatomic interaction of the Cu/Al2O3 interface which is reproduced on the basis of the results of rigid tensile tests of ab initio calculations. Next, we analyze the Cu/Al2O3 interface via a quasicontinuum model, using the interlayer potential identified above. The quasicontinuum model has been developed for large-scale atomistic simulations. In this approach, the number of degrees of freedom is much reduced in comparison to molecular dynamics, so that the computational time is significantly decreased. The atomistic-scale Cu/Al2O3 interface is investigated to determine the versatility of the quasicontinuum model. Relaxation simulations of the Cu/Al2O3 interface are carried out for both “large-scale analysis” and “small-scale analysis” via a quasicontinuum model. The influence of misfit in small-scale analysis is found to be much larger than the large-scale analysis upon comparing the displacement of atoms. We conclude that the results of the atomistic simulations with different sizes of the analytical region are strongly affected by the mechanical boundary conditions, and to obtain the accurate mechanical properties of interface, it is necessary to calculate with real size we subject of. The quasicontinuum method has great potential to realize an atomistic-continuum multiscale simulation. read less

Abstract: A cutting device has been developed by utilizing the scanning system of atomic force microscope (AFM) in machining, which aims at clarifying the ultimately small size removal as well as observing them in high resolution. As an application of the proposed method, the micro-chip deformation is investigated by cutting an amorphous metal Fe78B13Si9. It is shown that a lamellar structure, which is formed due to the localized shear occurred in a very narrow region and at very high strain rate, appears even at nanometer scale cutting. The simulation of this process using combined molecular dynamics (MD) and rigid-plastic finite element method (RPFEM) is also presented in this paper. The simulation shows that the localized shear would occur at the atomic scale by the cooperative group-movement of atoms. The high kinetic state of atoms would play a role of advancing this process for causing such localized shear. read less

Abstract: The spatial distribution of particles sputtered from the (001) face of Ni single-crystals is studied as a function of temperature. A significant increase in sputtering intensities both in the (011) directions and in random directions is found experimentally near the Curie point (T c = 635 K). The temperature dependence of mean-square angular deviation ψ2 of sputtered particles from close-packed (011) directions was determined both experimentally and by computer simulation. Except for a near-T c region, ψ2 increases linearly with temperature in agreement with the result of the computer calculation. At the Curie point, the experimental ψ2 has a sharp peak (corresponding to the value of ψ at 1200 K, determined by computer calculations). This result suggests a significant increase in displacement amplitude of surface atoms near T c, and gives a method for its estimation from sputtering patterns. read less

Abstract: This article has two primary objectives: to present a status report on our present understanding of the physics of atom ejection by ion bombardment and to indicate the contributions of molecular dynamics simulations to this research area. Because this application of molecular dynamics is relatively unfamiliar, basic simulation techniques useful in open systems are described in some detail. While this review discusses the current situation, explanations and historical background are necessarily included to place problems in perspective. read less

Abstract: In this paper we discuss the statics of small assemblies of soft, rare-gas type atoms (N=4 to 13) interacting under simple two-body central forces such as the Lennard-Jones and Morse type. Our main concern is to characterize the problem of isomer multiplicity in small packed structures and to devise practical algorithms for the discovery of a representative majority, if not all, stable soft-packing structures for clusters of atoms in the above size-range. We illustrate one such possible ‘Aufbau algorithm’ by demonstrating the existence of no less than 988 distinct, stable minimum configurations for 13 Lennard-Jones atoms and of correspondingly smaller numbers in the range N=7 to 12. The minimal structures obtained may be classified broadly into ‘crystallographic’ and ‘non-crystallographic’ types, the latter predominating among those of greatest binding energy. A surprising result is that, when the softer (α=3) Morse potential is used, the great majority of the Lennard-Jones minima are not support... read less

Abstract: A computer simulation of low energy implantation is presented. The method of calculation takes into account the inelastic processes and vacancies in the crystal lattice. The described simulation was used for a nitrogen implanted molybdenum single crystal. From the result of the calculation the possible positions of implanted nitrogen on the surface and in the bulk were obtained. The results of simulations are compared with those measured by SIMS and AES. read less

Abstract: AbstractPolycrystalline materials are visualized in this paper as a statistical ensemble of microelements whose crystallographic axes are randomly, but not uniform randomly, oriented in the material system. Based on this concept the influence of internal dislocations and grain boundaries on the elastic response of such metals is discussed. The latter influence is taken into consideration by combining the grain boundary coincidence cell models of Bollmann with the relaxation technique of Weins in the case of symmetric tilt boundaries. The micromechanics theory of Axelrad and Provan is also briefly discussed to indicate where these quantitative metallurgical studies are of importance in the further development of this theory. Resume Dans cette etude, les materiaux poly cristallins sont consideres comme un ensemble statistique de micro-elements dont les axes cristallographiques sont orientes au hasard, mais non uniformement, dans le materiau. A partir de ce concept, les auteurs discutent de l'influence de di... read less

Abstract: Migration energies of vacancies in aluminium and lithium have been calculated using an interatomic potential determined by an OPW pseudopotential method. This differs from potentials of the Born-Mayer and Morse types in that it is an oscillating potential, taking into account directly the ion-electron-ion interactions and stability of the crystal. The method of calculation is that of computer simulation of a section of lattice containing the vacancy in different stages of its migration, convergence and kinetic disturbance propagation criteria determining the volume of lattice permitted to relax around the defect. The effect of the oscillating potential is described and the results are reviewed In the light of its relative accuracy in the two metals chosen. read less

Abstract: The core structure and Peierls barrier for an edge dislocation lying in the {110} plane with Burgers vector along 〈111〉 in body-centered cubic iron were investigated numerically with the aid of a high speed computer using an anharmonic potential. The core radius is about 5 A and the corresponding core energy is 2.7 eV per identity distance along the dislocation line (six atom planes). The Peierls barrier is about 0.03 eV and the Peierls stress for dislocation motion at absolute zero is computed to be 5.36 × 109 dyn/cm2 or 0.0066 of the shear modulus. Die Kernstruktur und Peierls-Barriere fur eine Stufenversetzung in der {110}-Ebene mit dem Burgersvektor in 〈111〉-Richtung in kubisch raumzentriertem Eisen wird mit einem elektronischen Rechenautomaten untersucht, wobei ein anharmonisches Potential benutzt wird. Der Kernradius betragt ungefahr 5 A und die entsprechende Kernenergie 2,7 eV pro Identitatsabstand langs der Versetzungslinie (sechs Atomebenen). Die Peierls-Barriere ist ungefahr 0,03 eV und die Peierls-Spannung fur Versetzungsbewegung beim absoluten Nullpunkt wird zu 5,36 × 109 dyn/cm2 oder 0,0066 des Schubmoduls berechnet. read less