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pair_buck_coul_msm.cpp
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Mon, Nov 11, 20:57

pair_buck_coul_msm.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.
------------------------------------------------------------------------- */
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "pair_buck_coul_msm.h"
#include "atom.h"
#include "comm.h"
#include "force.h"
#include "kspace.h"
#include "neighbor.h"
#include "neigh_list.h"
#include "math_const.h"
#include "memory.h"
#include "error.h"
using namespace LAMMPS_NS;
using namespace MathConst;
/* ---------------------------------------------------------------------- */
PairBuckCoulMSM::PairBuckCoulMSM(LAMMPS *lmp) : PairBuckCoulLong(lmp)
{
ewaldflag = pppmflag = 0;
msmflag = 1;
nmax = 0;
ftmp = NULL;
}
/* ---------------------------------------------------------------------- */
PairBuckCoulMSM::~PairBuckCoulMSM()
{
if (ftmp) memory->destroy(ftmp);
}
/* ---------------------------------------------------------------------- */
void PairBuckCoulMSM::compute(int eflag, int vflag)
{
int i,j,ii,jj,inum,jnum,itype,jtype;
double qtmp,xtmp,ytmp,ztmp,delx,dely,delz,evdwl,ecoul,fpair,fcoul;
double rsq,r2inv,r6inv,forcecoul,forcebuck,factor_coul,factor_lj;
double egamma,fgamma,prefactor;
double r,rexp;
int *ilist,*jlist,*numneigh,**firstneigh;
int eflag_old = eflag;
if (force->kspace->scalar_pressure_flag && vflag) {
if (vflag > 2)
error->all(FLERR,"Must use 'kspace_modify pressure/scalar no' "
"to obtain per-atom virial with kspace_style MSM");
if (atom->nmax > nmax) {
if (ftmp) memory->destroy(ftmp);
nmax = atom->nmax;
memory->create(ftmp,nmax,3,"pair:ftmp");
}
memset(&ftmp[0][0],0,nmax*3*sizeof(double));
// must switch on global energy computation if not already on
if (eflag == 0 || eflag == 2) {
eflag++;
}
}
evdwl = ecoul = 0.0;
if (eflag || vflag) ev_setup(eflag,vflag);
else evflag = vflag_fdotr = 0;
double **x = atom->x;
double **f = atom->f;
double *q = atom->q;
int *type = atom->type;
int nlocal = atom->nlocal;
double *special_coul = force->special_coul;
double *special_lj = force->special_lj;
int newton_pair = force->newton_pair;
double qqrd2e = force->qqrd2e;
inum = list->inum;
ilist = list->ilist;
numneigh = list->numneigh;
firstneigh = list->firstneigh;
// loop over neighbors of my atoms
for (ii = 0; ii < inum; ii++) {
i = ilist[ii];
qtmp = q[i];
xtmp = x[i][0];
ytmp = x[i][1];
ztmp = x[i][2];
itype = type[i];
jlist = firstneigh[i];
jnum = numneigh[i];
for (jj = 0; jj < jnum; jj++) {
j = jlist[jj];
factor_lj = special_lj[sbmask(j)];
factor_coul = special_coul[sbmask(j)];
j &= NEIGHMASK;
delx = xtmp - x[j][0];
dely = ytmp - x[j][1];
delz = ztmp - x[j][2];
rsq = delx*delx + dely*dely + delz*delz;
jtype = type[j];
if (rsq < cutsq[itype][jtype]) {
r2inv = 1.0/rsq;
r = sqrt(rsq);
if (rsq < cut_coulsq) {
prefactor = qqrd2e * qtmp*q[j]/r;
egamma = 1.0 - (r/cut_coul)*force->kspace->gamma(r/cut_coul);
fgamma = 1.0 + (rsq/cut_coulsq)*force->kspace->dgamma(r/cut_coul);
forcecoul = prefactor * fgamma;
if (factor_coul < 1.0) forcecoul -= (1.0-factor_coul)*prefactor;
} else forcecoul = 0.0;
if (rsq < cut_ljsq[itype][jtype]) {
r6inv = r2inv*r2inv*r2inv;
rexp = exp(-r*rhoinv[itype][jtype]);
forcebuck = buck1[itype][jtype]*r*rexp - buck2[itype][jtype]*r6inv;
} else forcebuck = 0.0;
if (!(force->kspace->scalar_pressure_flag && vflag)) {
fpair = (forcecoul + factor_lj*forcebuck) * r2inv;
f[i][0] += delx*fpair;
f[i][1] += dely*fpair;
f[i][2] += delz*fpair;
if (newton_pair || j < nlocal) {
f[j][0] -= delx*fpair;
f[j][1] -= dely*fpair;
f[j][2] -= delz*fpair;
}
} else {
// separate Buck and Coulombic forces
fpair = (factor_lj*forcebuck) * r2inv;
f[i][0] += delx*fpair;
f[i][1] += dely*fpair;
f[i][2] += delz*fpair;
if (newton_pair || j < nlocal) {
f[j][0] -= delx*fpair;
f[j][1] -= dely*fpair;
f[j][2] -= delz*fpair;
}
fcoul = (forcecoul) * r2inv;
ftmp[i][0] += delx*fcoul;
ftmp[i][1] += dely*fcoul;
ftmp[i][2] += delz*fcoul;
if (newton_pair || j < nlocal) {
ftmp[j][0] -= delx*fcoul;
ftmp[j][1] -= dely*fcoul;
ftmp[j][2] -= delz*fcoul;
}
}
if (eflag) {
if (rsq < cut_coulsq) {
ecoul = prefactor*egamma;
if (factor_coul < 1.0) ecoul -= (1.0-factor_coul)*prefactor;
} else ecoul = 0.0;
if (eflag_old && rsq < cut_ljsq[itype][jtype]) {
evdwl = a[itype][jtype]*rexp - c[itype][jtype]*r6inv -
offset[itype][jtype];
evdwl *= factor_lj;
} else evdwl = 0.0;
}
if (evflag) ev_tally(i,j,nlocal,newton_pair,
evdwl,ecoul,fpair,delx,dely,delz);
}
}
}
if (vflag_fdotr) virial_fdotr_compute();
if (force->kspace->scalar_pressure_flag && vflag) {
for (i = 0; i < 3; i++) virial[i] += force->pair->eng_coul/3.0;
for (int i = 0; i < nmax; i++) {
f[i][0] += ftmp[i][0];
f[i][1] += ftmp[i][1];
f[i][2] += ftmp[i][2];
}
}
}
/* ---------------------------------------------------------------------- */
double PairBuckCoulMSM::single(int i, int j, int itype, int jtype,
double rsq,
double factor_coul, double factor_lj,
double &fforce)
{
double r2inv,r6inv,r,rexp,egamma,fgamma,prefactor;
double forcecoul,forcebuck,phicoul,phibuck;
r2inv = 1.0/rsq;
if (rsq < cut_coulsq) {
r = sqrt(rsq);
prefactor = force->qqrd2e * atom->q[i]*atom->q[j]/r;
egamma = 1.0 - (r/cut_coul)*force->kspace->gamma(r/cut_coul);
fgamma = 1.0 + (rsq/cut_coulsq)*force->kspace->dgamma(r/cut_coul);
forcecoul = prefactor * fgamma;
if (factor_coul < 1.0) forcecoul -= (1.0-factor_coul)*prefactor;
} else forcecoul = 0.0;
if (rsq < cut_ljsq[itype][jtype]) {
r6inv = r2inv*r2inv*r2inv;
r = sqrt(rsq);
rexp = exp(-r*rhoinv[itype][jtype]);
forcebuck = buck1[itype][jtype]*r*rexp - buck2[itype][jtype]*r6inv;
} else forcebuck = 0.0;
fforce = (forcecoul + factor_lj*forcebuck) * r2inv;
double eng = 0.0;
if (rsq < cut_coulsq) {
phicoul = prefactor*egamma;
if (factor_coul < 1.0) phicoul -= (1.0-factor_coul)*prefactor;
eng += phicoul;
}
if (rsq < cut_ljsq[itype][jtype]) {
phibuck = a[itype][jtype]*rexp - c[itype][jtype]*r6inv -
offset[itype][jtype];
eng += factor_lj*phibuck;
}
return eng;
}
/* ---------------------------------------------------------------------- */
void *PairBuckCoulMSM::extract(const char *str, int &dim)
{
dim = 0;
if (strcmp(str,"cut_coul") == 0) return (void *) &cut_coul;
return NULL;
}

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