## cohesive-potential-energy-crystal

Property Definition (short name) A common way to refer to the Property Definition. Note there may be multiple Property Definitions with the same short name, to fully distinguish between Property Definitions the full Tag URI must be used (the Property Definition ID). cohesive-potential-energy-crystal tag:staff@noreply.openkim.org,2023-02-21:property/cohesive-potential-energy-crystal Equilibrium crystal structure and potential formation energy at zero temperature and applied stress Equilibrium structure and energy of a crystal at zero temperature and applied stress. The equilibrium structure is expressed as an AFLOW prototype label and its corresponding free parameters. The equilibrium may be stable or unstable. Multiple instances of this property with different free parameters may be reported for a given AFLOW prototype label, representing different stable or unstable equilibria. There is no guarantee that any instance of this property is the ground state of this system, not even when the configuration space is restricted to the specified crystal prototype label.The reported formation potential energy is the energy required to decompose the solid into its individual atomic constituents isolated from each other. This is defined as the energy of the crystal less the energies of the isolated atomic constituents. For solids composed of neutral atoms, the cohesive energy is computed relative to the energy of the isolated atoms, which is sometimes referred to as the 'cohesive energy'. For ionic solids, the energy is computed relative to the energy of the isolated ions, in which case the term 'lattice energy' is sometimes used instead of cohesive energy.Two values are reported, the formation-potential-energy-per-atom is the average energy per atom in the unit cell, the formation-potential-energy-per-formula is the energy per chemical formula, which reflects the relative ratio of elements in the primitive unit cell of the crystal. For a crystal containing a single chemical element (regardless of structure) this is the same as the formation-potential-energy-per-atom, e.g. for hcp Mg the chemical formula is Mg and the 'formation-potential-energy-per-formula' is per magnesium atom (even though the hcp primitive unit cell contains two atoms). For compounds the 'potential-formation-energy-per-formula' will depend on the stoichiometric formula, e.g. for MoS_2 (AB2-type compound) the energy is per MoS_2 unit (i.e. 3 times larger than the formation-potential-energy-per-atom value). The reported energies are actual energies (not the negative of the energy as commonly reported for cohesive energy), therefore these values will be negative for a crystal that is more stable than its isolated constituents. ilia ilia 2023-02-21 Property Definition Physics Validator Property Documentation Wiki
See the KIM Properties Framework for more detailed information.

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#### Property Definition Keys

Required Optional

#### a

type float true [] true The equilibrium 'a' lattice constant of the crystal structure as defined by the AFLOW standard. Relative values of other lattice parameters (if present) are given in the 'parameter-values' key.

#### formation-potential-energy-per-atom

type float true [] true Formation potential energy per atom of the crystal defined as follows: \Delta \bar{V}_{atom} = ( V(A_{N_A}B_{N_B}...) - [N_A V_{atom}(A) + N_B V_{atom}(B) + ...] )/(N_A + N_B ...), where \Delta \bar{V}_{atom} is the formation energy per atom, V(A_{N_A}B_{N_B}...) is the energy of (any) unit cell, V_{atom}(X) is the energy of an isolated atom of species X, and N_X is the number of atoms of species X in the (same) unit cell.

#### formation-potential-energy-per-formula

type float true [] true This variable has the same definition as 'formation-potential-energy-per-atom' except that the energy is normalized per chemical formula instead of per atom, i.e. \Delta \bar{V}_{formula} = \Delta \bar{V}_{atom} N_{formula}, where N_{formula} is the number of atoms in the reduced stoichiometric formula, i.e. the sum of indices in the first section of the prototype-label.

#### prototype-label

type string false [] true Prototype label (not including an enumeration suffix) as defined by the AFLOW standard (e.g. 'A_tI4_141_a') for the structure. It is expected that the alphabetically lowest of all equivalent labels is chosen.

#### stoichiometric-species

type string false [":"] true Element symbols corresponding to the atom types in the stoichiometric formula which appears at the start of the prototype label (e.g. ['Mo','S'] for the AB2 stoichiometric formula, means that the 'A' atom is 'Mo' and the 'B' atom is 'S' for the MoS_2 structure).

#### formation-potential-energy-type

type string false [] false The formation potential energy type, either 'cohesive' (default if key not provided) or 'lattice'. This indicates whether the energy is computed relative to a reference state of isolated neutral atoms ('cohesive'), or isolated ions ('lattice').

#### library-prototype-label

type string false [] false The AFLOW library prototype, if any, matching the equilibrium structure. Prototypes in the AFLOW library are associated with common short names used by the materials community. The library prototype includes an integer enumeration suffix defined by the AFLOW standard when there are multiple parameter values associated with the structure (e.g. 'A_tI4_141_a-001' for 'betaSn'). Because these prototype labels are named according to their original material's conventional chemical formula, they may differ from the 'prototype-label' key, which is expected to be standardized to have the alphabetically lowest possible of all equivalent labels.

#### parameter-names

type string false [":"] false Names of the parameters other than 'a', if present, corresponding to this AFLOW prototype. These can include lattice parameters from the set {'b/a','c/a','alpha','beta','gamma'} (for the conventional crystal structure defined by lattice parameters a, b, and c and angles alpha, beta, gamma), and coordinates of Wyckoff positions that have a degree of variability labeled as 'x*', 'y*' and 'z*' where the asterisk represents an integer as defined by the AFLOW standard.

#### parameter-values

type float false [":"] false Equilibrium values for the parameters listed in 'parameter-names'. Note that all parameters are dimensionless.

#### short-name

type string false [] false Commonly used name associated with the 'library-prototype-label' key according to the AFLOW prototype library (e.g. 'Face-Centered Cubic' or 'Molybdenite').

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