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pair_coul_dsf.cpp
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Wed, Nov 13, 05:54

pair_coul_dsf.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: Trung Dac Nguyen (ORNL)
References: Fennell and Gezelter, JCP 124, 234104 (2006)
------------------------------------------------------------------------- */
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "pair_coul_dsf.h"
#include "atom.h"
#include "comm.h"
#include "force.h"
#include "neighbor.h"
#include "neigh_list.h"
#include "memory.h"
#include "math_const.h"
#include "error.h"
using namespace LAMMPS_NS;
using namespace MathConst;
#define EWALD_F 1.12837917
#define EWALD_P 0.3275911
#define A1 0.254829592
#define A2 -0.284496736
#define A3 1.421413741
#define A4 -1.453152027
#define A5 1.061405429
/* ---------------------------------------------------------------------- */
PairCoulDSF::PairCoulDSF(LAMMPS *lmp) : Pair(lmp)
{
single_enable = 0;
}
/* ---------------------------------------------------------------------- */
PairCoulDSF::~PairCoulDSF()
{
if (copymode) return;
if (allocated) {
memory->destroy(setflag);
memory->destroy(cutsq);
}
}
/* ---------------------------------------------------------------------- */
void PairCoulDSF::compute(int eflag, int vflag)
{
int i,j,ii,jj,inum,jnum;
double qtmp,xtmp,ytmp,ztmp,delx,dely,delz,ecoul,fpair;
double r,rsq,r2inv,forcecoul,factor_coul;
double prefactor,erfcc,erfcd,t;
int *ilist,*jlist,*numneigh,**firstneigh;
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 nlocal = atom->nlocal;
double *special_coul = force->special_coul;
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];
jlist = firstneigh[i];
jnum = numneigh[i];
if (eflag) {
double e_self = -(e_shift/2.0 + alpha/MY_PIS) * qtmp*qtmp*qqrd2e;
ev_tally(i,i,nlocal,0,0.0,e_self,0.0,0.0,0.0,0.0);
}
for (jj = 0; jj < jnum; jj++) {
j = jlist[jj];
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;
if (rsq < cut_coulsq) {
r2inv = 1.0/rsq;
r = sqrt(rsq);
prefactor = qqrd2e*qtmp*q[j]/r;
erfcd = exp(-alpha*alpha*rsq);
t = 1.0 / (1.0 + EWALD_P*alpha*r);
erfcc = t * (A1+t*(A2+t*(A3+t*(A4+t*A5)))) * erfcd;
forcecoul = prefactor * (erfcc/r + 2.0*alpha/MY_PIS * erfcd +
r*f_shift) * r;
if (factor_coul < 1.0) forcecoul -= (1.0-factor_coul)*prefactor;
fpair = forcecoul * 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;
}
if (eflag) {
ecoul = prefactor * (erfcc - r*e_shift - rsq*f_shift);
if (factor_coul < 1.0) ecoul -= (1.0-factor_coul)*prefactor;
} else ecoul = 0.0;
if (evflag) ev_tally(i,j,nlocal,newton_pair,
0.0,ecoul,fpair,delx,dely,delz);
}
}
}
if (vflag_fdotr) virial_fdotr_compute();
}
/* ----------------------------------------------------------------------
allocate all arrays
------------------------------------------------------------------------- */
void PairCoulDSF::allocate()
{
allocated = 1;
int n = atom->ntypes;
memory->create(setflag,n+1,n+1,"pair:setflag");
for (int i = 1; i <= n; i++)
for (int j = i; j <= n; j++)
setflag[i][j] = 0;
memory->create(cutsq,n+1,n+1,"pair:cutsq");
}
/* ----------------------------------------------------------------------
global settings
------------------------------------------------------------------------- */
void PairCoulDSF::settings(int narg, char **arg)
{
if (narg != 2) error->all(FLERR,"Illegal pair_style command");
alpha = force->numeric(FLERR,arg[0]);
cut_coul = force->numeric(FLERR,arg[1]);
}
/* ----------------------------------------------------------------------
set coeffs for one or more type pairs
------------------------------------------------------------------------- */
void PairCoulDSF::coeff(int narg, char **arg)
{
if (narg != 2) error->all(FLERR,"Incorrect args for pair coefficients");
if (!allocated) allocate();
int ilo,ihi,jlo,jhi;
force->bounds(arg[0],atom->ntypes,ilo,ihi);
force->bounds(arg[1],atom->ntypes,jlo,jhi);
int count = 0;
for (int i = ilo; i <= ihi; i++) {
for (int j = MAX(jlo,i); j <= jhi; j++) {
setflag[i][j] = 1;
count++;
}
}
if (count == 0) error->all(FLERR,"Incorrect args for pair coefficients");
}
/* ----------------------------------------------------------------------
init specific to this pair style
------------------------------------------------------------------------- */
void PairCoulDSF::init_style()
{
if (!atom->q_flag)
error->all(FLERR,"Pair style coul/dsf requires atom attribute q");
neighbor->request(this,instance_me);
cut_coulsq = cut_coul * cut_coul;
double erfcc = erfc(alpha*cut_coul);
double erfcd = exp(-alpha*alpha*cut_coul*cut_coul);
f_shift = -(erfcc/cut_coulsq + 2.0/MY_PIS*alpha*erfcd/cut_coul);
e_shift = erfcc/cut_coul - f_shift*cut_coul;
}
/* ----------------------------------------------------------------------
init for one type pair i,j and corresponding j,i
------------------------------------------------------------------------- */
double PairCoulDSF::init_one(int i, int j)
{
return cut_coul;
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void PairCoulDSF::write_restart(FILE *fp)
{
write_restart_settings(fp);
int i,j;
for (i = 1; i <= atom->ntypes; i++)
for (j = i; j <= atom->ntypes; j++) {
fwrite(&setflag[i][j],sizeof(int),1,fp);
}
}
/* ----------------------------------------------------------------------
proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */
void PairCoulDSF::read_restart(FILE *fp)
{
read_restart_settings(fp);
allocate();
int i,j;
int me = comm->me;
for (i = 1; i <= atom->ntypes; i++)
for (j = i; j <= atom->ntypes; j++) {
if (me == 0) fread(&setflag[i][j],sizeof(int),1,fp);
MPI_Bcast(&setflag[i][j],1,MPI_INT,0,world);
}
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void PairCoulDSF::write_restart_settings(FILE *fp)
{
fwrite(&alpha,sizeof(double),1,fp);
fwrite(&cut_coul,sizeof(double),1,fp);
fwrite(&offset_flag,sizeof(int),1,fp);
fwrite(&mix_flag,sizeof(int),1,fp);
}
/* ----------------------------------------------------------------------
proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */
void PairCoulDSF::read_restart_settings(FILE *fp)
{
if (comm->me == 0) {
fread(&alpha,sizeof(double),1,fp);
fread(&cut_coul,sizeof(double),1,fp);
fread(&offset_flag,sizeof(int),1,fp);
fread(&mix_flag,sizeof(int),1,fp);
}
MPI_Bcast(&alpha,1,MPI_DOUBLE,0,world);
MPI_Bcast(&cut_coul,1,MPI_DOUBLE,0,world);
MPI_Bcast(&offset_flag,1,MPI_INT,0,world);
MPI_Bcast(&mix_flag,1,MPI_INT,0,world);
}
/* ---------------------------------------------------------------------- */
double PairCoulDSF::single(int i, int j, int itype, int jtype, double rsq,
double factor_coul, double factor_lj,
double &fforce)
{
double r2inv,r,erfcc,erfcd,prefactor,t;
double forcecoul,phicoul;
r2inv = 1.0/rsq;
double eng = 0.0;
if (rsq < cut_coulsq) {
r = sqrt(rsq);
prefactor = factor_coul * force->qqrd2e * atom->q[i]*atom->q[j]/r;
erfcd = exp(-alpha*alpha*rsq);
t = 1.0 / (1.0 + EWALD_P*alpha*r);
erfcc = t * (A1+t*(A2+t*(A3+t*(A4+t*A5)))) * erfcd;
forcecoul = prefactor * (erfcc/r + 2.0*alpha/MY_PIS*erfcd +
r*f_shift) * r;
phicoul = prefactor * (erfcc - r*e_shift - rsq*f_shift);
eng += phicoul;
} else forcecoul = 0.0;
fforce = forcecoul * r2inv;
return eng;
}
/* ---------------------------------------------------------------------- */
void *PairCoulDSF::extract(const char *str, int &dim)
{
if (strcmp(str,"cut_coul") == 0) {
dim = 0;
return (void *) &cut_coul;
}
return NULL;
}

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