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pair_tersoff_mod.cpp
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Wed, Nov 6, 06:23

pair_tersoff_mod.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
http://lammps.sandia.gov, Sandia National Laboratories
Steve Plimpton, sjplimp@sandia.gov
Copyright (2003) Sandia Corporation. Under the terms of Contract
DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
certain rights in this software. This software is distributed under
the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
Contributing author: Aidan Thompson (SNL) - original Tersoff implementation
Vitaly Dozhdikov (JIHT of RAS) - MOD addition
------------------------------------------------------------------------- */
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "pair_tersoff_mod.h"
#include "atom.h"
#include "neighbor.h"
#include "neigh_list.h"
#include "neigh_request.h"
#include "force.h"
#include "comm.h"
#include "memory.h"
#include "error.h"
#include "math_const.h"
using namespace LAMMPS_NS;
using namespace MathConst;
#define MAXLINE 1024
#define DELTA 4
/* ---------------------------------------------------------------------- */
PairTersoffMOD::PairTersoffMOD(LAMMPS *lmp) : PairTersoff(lmp) {}
/* ---------------------------------------------------------------------- */
void PairTersoffMOD::read_file(char *file)
{
int params_per_line = 20;
char **words = new char*[params_per_line+1];
memory->sfree(params);
params = NULL;
nparams = maxparam = 0;
// open file on proc 0
FILE *fp;
if (comm->me == 0) {
fp = force->open_potential(file);
if (fp == NULL) {
char str[128];
sprintf(str,"Cannot open Tersoff potential file %s",file);
error->one(FLERR,str);
}
}
// read each line out of file, skipping blank lines or leading '#'
// store line of params if all 3 element tags are in element list
int n,nwords,ielement,jelement,kelement;
char line[MAXLINE],*ptr;
int eof = 0;
while (1) {
if (comm->me == 0) {
ptr = fgets(line,MAXLINE,fp);
if (ptr == NULL) {
eof = 1;
fclose(fp);
} else n = strlen(line) + 1;
}
MPI_Bcast(&eof,1,MPI_INT,0,world);
if (eof) break;
MPI_Bcast(&n,1,MPI_INT,0,world);
MPI_Bcast(line,n,MPI_CHAR,0,world);
// strip comment, skip line if blank
if ((ptr = strchr(line,'#'))) *ptr = '\0';
nwords = atom->count_words(line);
if (nwords == 0) continue;
// concatenate additional lines until have params_per_line words
while (nwords < params_per_line) {
n = strlen(line);
if (comm->me == 0) {
ptr = fgets(&line[n],MAXLINE-n,fp);
if (ptr == NULL) {
eof = 1;
fclose(fp);
} else n = strlen(line) + 1;
}
MPI_Bcast(&eof,1,MPI_INT,0,world);
if (eof) break;
MPI_Bcast(&n,1,MPI_INT,0,world);
MPI_Bcast(line,n,MPI_CHAR,0,world);
if ((ptr = strchr(line,'#'))) *ptr = '\0';
nwords = atom->count_words(line);
}
if (nwords != params_per_line)
error->all(FLERR,"Incorrect format in Tersoff potential file");
// words = ptrs to all words in line
nwords = 0;
words[nwords++] = strtok(line," \t\n\r\f");
while ((words[nwords++] = strtok(NULL," \t\n\r\f"))) continue;
// ielement,jelement,kelement = 1st args
// if all 3 args are in element list, then parse this line
// else skip to next line
for (ielement = 0; ielement < nelements; ielement++)
if (strcmp(words[0],elements[ielement]) == 0) break;
if (ielement == nelements) continue;
for (jelement = 0; jelement < nelements; jelement++)
if (strcmp(words[1],elements[jelement]) == 0) break;
if (jelement == nelements) continue;
for (kelement = 0; kelement < nelements; kelement++)
if (strcmp(words[2],elements[kelement]) == 0) break;
if (kelement == nelements) continue;
// load up parameter settings and error check their values
if (nparams == maxparam) {
maxparam += DELTA;
params = (Param *) memory->srealloc(params,maxparam*sizeof(Param),
"pair:params");
}
params[nparams].ielement = ielement;
params[nparams].jelement = jelement;
params[nparams].kelement = kelement;
params[nparams].powerm = atof(words[3]);
params[nparams].lam3 = atof(words[4]);
params[nparams].h = atof(words[5]);
params[nparams].powern = atof(words[6]);
params[nparams].beta = atof(words[7]);
params[nparams].lam2 = atof(words[8]);
params[nparams].bigb = atof(words[9]);
params[nparams].bigr = atof(words[10]);
params[nparams].bigd = atof(words[11]);
params[nparams].lam1 = atof(words[12]);
params[nparams].biga = atof(words[13]);
params[nparams].powern_del = atof(words[14]);
params[nparams].c1 = atof(words[15]);
params[nparams].c2 = atof(words[16]);
params[nparams].c3 = atof(words[17]);
params[nparams].c4 = atof(words[18]);
params[nparams].c5 = atof(words[19]);
// currently only allow m exponent of 1
params[nparams].powermint = int(params[nparams].powerm);
if (
params[nparams].lam3 < 0.0 || params[nparams].powern < 0.0 ||
params[nparams].beta < 0.0 || params[nparams].lam2 < 0.0 ||
params[nparams].bigb < 0.0 || params[nparams].bigr < 0.0 ||
params[nparams].bigd < 0.0 ||
params[nparams].bigd > params[nparams].bigr ||
params[nparams].lam3 < 0.0 || params[nparams].biga < 0.0 ||
params[nparams].powerm - params[nparams].powermint != 0.0 ||
(params[nparams].powermint != 3 && params[nparams].powermint != 1))
error->all(FLERR,"Illegal Tersoff parameter");
nparams++;
}
delete [] words;
}
/* ---------------------------------------------------------------------- */
void PairTersoffMOD::setup_params()
{
int i,j,k,m,n;
// set elem2param for all element triplet combinations
// must be a single exact match to lines read from file
// do not allow for ACB in place of ABC
memory->destroy(elem2param);
memory->create(elem2param,nelements,nelements,nelements,"pair:elem2param");
for (i = 0; i < nelements; i++)
for (j = 0; j < nelements; j++)
for (k = 0; k < nelements; k++) {
n = -1;
for (m = 0; m < nparams; m++) {
if (i == params[m].ielement && j == params[m].jelement &&
k == params[m].kelement) {
if (n >= 0) error->all(FLERR,"Potential file has duplicate entry");
n = m;
}
}
if (n < 0) error->all(FLERR,"Potential file is missing an entry");
elem2param[i][j][k] = n;
}
// compute parameter values derived from inputs
for (m = 0; m < nparams; m++) {
params[m].cut = params[m].bigr + params[m].bigd;
params[m].cutsq = params[m].cut*params[m].cut;
params[m].ca1 = pow(2.0*params[m].powern_del*1.0e-16,-1.0/params[m].powern);
params[m].ca4 = 1.0/params[m].ca1;
}
// set cutmax to max of all params
cutmax = 0.0;
for (m = 0; m < nparams; m++)
if (params[m].cut > cutmax) cutmax = params[m].cut;
}
/* ---------------------------------------------------------------------- */
double PairTersoffMOD::zeta(Param *param, double rsqij, double rsqik,
double *delrij, double *delrik)
{
double rij,rik,costheta,arg,ex_delr;
rij = sqrt(rsqij);
rik = sqrt(rsqik);
costheta = (delrij[0]*delrik[0] + delrij[1]*delrik[1] +
delrij[2]*delrik[2]) / (rij*rik);
if (param->powermint == 3) arg = pow(param->lam3 * (rij-rik),3.0);
else arg = param->lam3 * (rij-rik);
if (arg > 69.0776) ex_delr = 1.e30;
else if (arg < -69.0776) ex_delr = 0.0;
else ex_delr = exp(arg);
return ters_fc(rik,param) * ters_gijk_mod(costheta,param) * ex_delr;
}
/* ---------------------------------------------------------------------- */
double PairTersoffMOD::ters_fc(double r, Param *param)
{
double ters_R = param->bigr;
double ters_D = param->bigd;
if (r < ters_R-ters_D) return 1.0;
if (r > ters_R+ters_D) return 0.0;
return 0.5*(1.0 - 1.125*sin(MY_PI2*(r - ters_R)/ters_D) -
0.125*sin(3*MY_PI2*(r - ters_R)/ters_D));
}
/* ---------------------------------------------------------------------- */
double PairTersoffMOD::ters_fc_d(double r, Param *param)
{
double ters_R = param->bigr;
double ters_D = param->bigd;
if (r < ters_R-ters_D) return 0.0;
if (r > ters_R+ters_D) return 0.0;
return -(0.375*MY_PI4/ters_D) * (3*cos(MY_PI2*(r - ters_R)/ters_D) +
cos(3*MY_PI2*(r - ters_R)/ters_D));
}
/* ---------------------------------------------------------------------- */
double PairTersoffMOD::ters_bij(double zeta, Param *param)
{
double tmp = param->beta * zeta;
if (tmp > param->ca1) return pow(tmp, -param->powern/(2.0*param->powern_del));
if (tmp < param->ca4) return 1.0;
return pow(1.0 + pow(tmp,param->powern), -1.0/(2.0*param->powern_del));
}
/* ---------------------------------------------------------------------- */
double PairTersoffMOD::ters_bij_d(double zeta, Param *param)
{
double tmp = param->beta * zeta;
if (tmp > param->ca1) return -0.5*(param->powern/param->powern_del)*
pow(tmp,-0.5*(param->powern/param->powern_del)) / zeta;
if (tmp < param->ca4) return 0.0;
double tmp_n = pow(tmp,param->powern);
return -0.5 *(param->powern/param->powern_del)*
pow(1.0+tmp_n, -1.0-(1.0/(2.0*param->powern_del)))*tmp_n / zeta;
}
/* ---------------------------------------------------------------------- */
void PairTersoffMOD::ters_zetaterm_d(double prefactor,
double *rij_hat, double rij,
double *rik_hat, double rik,
double *dri, double *drj, double *drk,
Param *param)
{
double gijk,gijk_d,ex_delr,ex_delr_d,fc,dfc,cos_theta,tmp;
double dcosdri[3],dcosdrj[3],dcosdrk[3];
fc = ters_fc(rik,param);
dfc = ters_fc_d(rik,param);
if (param->powermint == 3) tmp = pow(param->lam3 * (rij-rik),3.0);
else tmp = param->lam3 * (rij-rik);
if (tmp > 69.0776) ex_delr = 1.e30;
else if (tmp < -69.0776) ex_delr = 0.0;
else ex_delr = exp(tmp);
if (param->powermint == 3)
ex_delr_d = 3.0*pow(param->lam3,3.0) * pow(rij-rik,2.0)*ex_delr;
else ex_delr_d = param->lam3 * ex_delr;
cos_theta = vec3_dot(rij_hat,rik_hat);
gijk = ters_gijk_mod(cos_theta,param);
gijk_d = ters_gijk_d_mod(cos_theta,param);
costheta_d(rij_hat,rij,rik_hat,rik,dcosdri,dcosdrj,dcosdrk);
// compute the derivative wrt Ri
// dri = -dfc*gijk*ex_delr*rik_hat;
// dri += fc*gijk_d*ex_delr*dcosdri;
// dri += fc*gijk*ex_delr_d*(rik_hat - rij_hat);
vec3_scale(-dfc*gijk*ex_delr,rik_hat,dri);
vec3_scaleadd(fc*gijk_d*ex_delr,dcosdri,dri,dri);
vec3_scaleadd(fc*gijk*ex_delr_d,rik_hat,dri,dri);
vec3_scaleadd(-fc*gijk*ex_delr_d,rij_hat,dri,dri);
vec3_scale(prefactor,dri,dri);
// compute the derivative wrt Rj
// drj = fc*gijk_d*ex_delr*dcosdrj;
// drj += fc*gijk*ex_delr_d*rij_hat;
vec3_scale(fc*gijk_d*ex_delr,dcosdrj,drj);
vec3_scaleadd(fc*gijk*ex_delr_d,rij_hat,drj,drj);
vec3_scale(prefactor,drj,drj);
// compute the derivative wrt Rk
// drk = dfc*gijk*ex_delr*rik_hat;
// drk += fc*gijk_d*ex_delr*dcosdrk;
// drk += -fc*gijk*ex_delr_d*rik_hat;
vec3_scale(dfc*gijk*ex_delr,rik_hat,drk);
vec3_scaleadd(fc*gijk_d*ex_delr,dcosdrk,drk,drk);
vec3_scaleadd(-fc*gijk*ex_delr_d,rik_hat,drk,drk);
vec3_scale(prefactor,drk,drk);
}

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