/* */ /* CDDL HEADER START */ /* */ /* The contents of this file are subject to the terms of the Common */ /* Development and Distribution License Version 1.0 (the "License"). */ /* */ /* You can obtain a copy of the license at */ /* http://www.opensource.org/licenses/CDDL-1.0. See the License for the */ /* specific language governing permissions and limitations under the License. */ /* */ /* When distributing Covered Code, include this CDDL HEADER in each file and */ /* include the License file in a prominent location with the name */ /* LICENSE.CDDL. If applicable, add the following below this CDDL HEADER, */ /* with the fields enclosed by brackets "[]" replaced with your own */ /* identifying information: */ /* */ /* Portions Copyright (c) [yyyy] [name of copyright owner]. */ /* All rights reserved. */ /* */ /* CDDL HEADER END */ /* */ /* */ /* Portions Copyright (c) 2019, Regents of the University of Minnesota. */ /* All rights reserved. */ /* */ /* Contributors: */ /* Daniel S. Karls */ /* Ellad B. Tadmor */ /* Ryan S. Elliott */ /* Ben C. Druecke */ /* */ #include /* */ /* Model driver for the Stephenson-Radny-Smith (SRS) potential */ /* */ /* Source: */ /* P. C. L. Stephenson, M. W. Radny and P. V. Smith, */ /* "A modified Stillinger-Weber potential for modeling silicon surfaces", */ /* Surface Science, Vol. 366, 177-184, 1996. */ /* */ /* The following flag indicates whether or not to do an explicit check to */ /* determine if the distance between neighbors j and k of atom i in a */ /* three-body computations exceeds the (single) cutoff distance. The check */ /* is skipped if the flag is set to 1, and performed if the flag is set to 0. */ /* This feature is provided for efficiency reasons. */ /* */ #define SKIP_CHECK_ON_RJK 1 /* The following enumeration provides a named index to each element in your */ /* parameter array. The last entry *must* be NUM_PARAMS (by construction by */ /* being at the end of the list, its value will be the number of parameters). */ /* These names will be used in the functions below to unpack and access */ /* parameters. The order of parameters *is* important. It must match the */ /* ordering in the parameter file read in by the model driver. */ /* */ enum PARAMS { PARAM_A, PARAM_B, PARAM_p, PARAM_q, PARAM_a, PARAM_lambda, PARAM_gamma, PARAM_zeta, PARAM_b, PARAM_k, PARAM_c, PARAM_sigma, PARAM_epsilon, NUM_PARAMS }; #include "cluster_aux.inc" /* The following array of strings contains names and descriptions of the */ /* parameters that will be registered in the KIM API object. The number of */ /* entries must match the number of PARAM_* lines above, and the order must */ /* correspond to the ordering above. */ /* */ static char const * const param_strings[][2] = {{"A", "Amplitude of the pairwise interaction function"}, {"B", "Prefactor of r^-p in pairwise term"}, {"p", "Exponent in the r^-p term in the pairwise interaction"}, {"q", "Exponent in the r^-q term in the pairwise interaction"}, {"a", "Non-dimensionalized cutoff distance appearing in the exponential cutoff function"}, {"lambda", "Amplitude of the Stillinger-Weber h-function appearing int the three-body term"}, {"gamma", "Scaling factor in numerator of terms inside the exponential cutoff function"}, {"zeta", "Numerator of argument of exponential in pairwise interaction"}, {"b", "Amplitude factor in angular dependence in three-body term"}, {"k", "Factor governing equilibrium angle in three-body term: cos(theta)=-k"}, {"c", "Offset in amplitude of angular dependence term"}, {"sigma", "Length scale"}, {"epsilon", "Energy scale"}}; /* The following two variables define the base unit system required to be */ /* used by the parameter file. */ /* */ static KIM_LengthUnit const * const length_unit = &KIM_LENGTH_UNIT_A; static KIM_EnergyUnit const * const energy_unit = &KIM_ENERGY_UNIT_eV; /* The following array of double precision values define the unit */ /* exponents for each parameter. The first number is the length exponent */ /* and the second number is the energy exponent. The number of entries must */ /* match the number of PARAM_* lines above, and the order must correspond */ /* to the ordering above. Use two zeros for unitless parameters. */ /* */ static double const param_units[][2] = {{0.0, 0.0}, /* A */ {0.0, 0.0}, /* B */ {0.0, 0.0}, /* p */ {0.0, 0.0}, /* q */ {0.0, 0.0}, /* a */ {0.0, 0.0}, /* lambda */ {0.0, 0.0}, /* gamma */ {0.0, 0.0}, /* zeta */ {0.0, 0.0}, /* b */ {0.0, 0.0}, /* k */ {0.0, 0.0}, /* c */ {1.0, 0.0}, /* sigma */ {0.0, 1.0}}; /* epsilon */ /* Function: get_influence_distance */ /* Description: Sets the largest distance at which a neighbor can affect the */ /* energy of another atom. */ static double get_influence_distance(double const * const params) { double const a = params[PARAM_a]; double const sigma = params[PARAM_sigma]; return sigma * a; } /* Calculate two-body energy phi2(r) and its derivative w.r.t. Rij */ static void calc_phi2_dphi2(double const * const params, double const Rij, double * const phi2, double * const dphi2_dRij) { /* Unpack parameters */ double const epsilon = params[PARAM_epsilon]; double const sigma = params[PARAM_sigma]; double f2val; double df2_dRij; f2_df2(params, Rij / sigma, &f2val, &df2_dRij); *phi2 = epsilon * f2val; if (dphi2_dRij != NULL) { *dphi2_dRij = epsilon * df2_dRij / sigma; } return; } /* Calculate three-body energy phi3(Rij, Rik, Rjk) and its derivatives w.r.t Rij, Rik, and Rjk */ static void calc_phi3_dphi3(double const * const params, double const Rij, double const Rik, double const Rjk, double * const phi3, double * const dphi3_dRij, double * const dphi3_dRik, double * const dphi3_dRjk) { /* Unpack parameters */ double const epsilon = params[PARAM_epsilon]; double const sigma = params[PARAM_sigma]; double f3val; double df3_dRij; double df3_dRik; double df3_dRjk; f3_df3(params, Rij / sigma, Rik / sigma, Rjk / sigma, &f3val, &df3_dRij, &df3_dRik, &df3_dRjk); *phi3 = epsilon * f3val; if (dphi3_dRij != NULL) { *dphi3_dRij = epsilon * df3_dRij / sigma; *dphi3_dRik = epsilon * df3_dRik / sigma; *dphi3_dRjk = epsilon * df3_dRjk / sigma; } return; }