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pair_born_coul_long.cpp
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Fri, Jun 21, 19:20

pair_born_coul_long.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: Ahmed Ismail (SNL)
------------------------------------------------------------------------- */
#include "math.h"
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "pair_born_coul_long.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;
#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
/* ---------------------------------------------------------------------- */
PairBornCoulLong::PairBornCoulLong(LAMMPS *lmp) : Pair(lmp)
{
ewaldflag = pppmflag = 1;
ftable = NULL;
}
/* ---------------------------------------------------------------------- */
PairBornCoulLong::~PairBornCoulLong()
{
if (allocated) {
memory->destroy(setflag);
memory->destroy(cutsq);
memory->destroy(cut_lj);
memory->destroy(cut_ljsq);
memory->destroy(a);
memory->destroy(rho);
memory->destroy(sigma);
memory->destroy(c);
memory->destroy(d);
memory->destroy(rhoinv);
memory->destroy(born1);
memory->destroy(born2);
memory->destroy(born3);
memory->destroy(offset);
}
if (ftable) free_tables();
}
/* ---------------------------------------------------------------------- */
void PairBornCoulLong::compute(int eflag, int vflag)
{
int i,j,ii,jj,inum,jnum,itable,itype,jtype;
double qtmp,xtmp,ytmp,ztmp,delx,dely,delz,evdwl,ecoul,fpair;
double fraction,table;
double rsq,r2inv,r6inv,forcecoul,forceborn,factor_coul,factor_lj;
double grij,expm2,prefactor,t,erfc;
double r,rexp;
int *ilist,*jlist,*numneigh,**firstneigh;
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;
if (rsq < cut_coulsq) {
if (!ncoultablebits || rsq <= tabinnersq) {
r = sqrt(rsq);
grij = g_ewald * r;
expm2 = exp(-grij*grij);
t = 1.0 / (1.0 + EWALD_P*grij);
erfc = t * (A1+t*(A2+t*(A3+t*(A4+t*A5)))) * expm2;
prefactor = qqrd2e * qtmp*q[j]/r;
forcecoul = prefactor * (erfc + EWALD_F*grij*expm2);
if (factor_coul < 1.0) forcecoul -= (1.0-factor_coul)*prefactor;
} else {
union_int_float_t rsq_lookup;
rsq_lookup.f = rsq;
itable = rsq_lookup.i & ncoulmask;
itable >>= ncoulshiftbits;
fraction = (rsq_lookup.f - rtable[itable]) * drtable[itable];
table = ftable[itable] + fraction*dftable[itable];
forcecoul = qtmp*q[j] * table;
if (factor_coul < 1.0) {
table = ctable[itable] + fraction*dctable[itable];
prefactor = qtmp*q[j] * table;
forcecoul -= (1.0-factor_coul)*prefactor;
}
}
} else forcecoul = 0.0;
if (rsq < cut_ljsq[itype][jtype]) {
r = sqrt(rsq);
r6inv = r2inv*r2inv*r2inv;
rexp = exp((sigma[itype][jtype]-r)*rhoinv[itype][jtype]);
forceborn = born1[itype][jtype]*r*rexp - born2[itype][jtype]*r6inv
+ born3[itype][jtype]*r2inv*r6inv;
} else forceborn = 0.0;
fpair = (forcecoul + factor_lj*forceborn) * 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) {
if (rsq < cut_coulsq) {
if (!ncoultablebits || rsq <= tabinnersq)
ecoul = prefactor*erfc;
else {
table = etable[itable] + fraction*detable[itable];
ecoul = qtmp*q[j] * table;
}
if (factor_coul < 1.0) ecoul -= (1.0-factor_coul)*prefactor;
} else ecoul = 0.0;
if (rsq < cut_ljsq[itype][jtype]) {
evdwl = a[itype][jtype]*rexp - c[itype][jtype]*r6inv
+ d[itype][jtype]*r6inv*r2inv - 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();
}
/* ----------------------------------------------------------------------
allocate all arrays
------------------------------------------------------------------------- */
void PairBornCoulLong::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");
memory->create(cut_lj,n+1,n+1,"pair:cut_lj");
memory->create(cut_ljsq,n+1,n+1,"pair:cut_ljsq");
memory->create(a,n+1,n+1,"pair:a");
memory->create(rho,n+1,n+1,"pair:rho");
memory->create(sigma,n+1,n+1,"pair:sigma");
memory->create(c,n+1,n+1,"pair:c");
memory->create(d,n+1,n+1,"pair:d");
memory->create(rhoinv,n+1,n+1,"pair:rhoinv");
memory->create(born1,n+1,n+1,"pair:born1");
memory->create(born2,n+1,n+1,"pair:born2");
memory->create(born3,n+1,n+1,"pair:born3");
memory->create(offset,n+1,n+1,"pair:offset");
}
/* ----------------------------------------------------------------------
global settings
------------------------------------------------------------------------- */
void PairBornCoulLong::settings(int narg, char **arg)
{
if (narg < 1 || narg > 2) error->all(FLERR,"Illegal pair_style command");
cut_lj_global = force->numeric(arg[0]);
if (narg == 1) cut_coul = cut_lj_global;
else cut_coul = force->numeric(arg[1]);
// reset cutoffs that have been explicitly set
if (allocated) {
int i,j;
for (i = 1; i <= atom->ntypes; i++)
for (j = i+1; j <= atom->ntypes; j++)
if (setflag[i][j]) cut_lj[i][j] = cut_lj_global;
}
}
/* ----------------------------------------------------------------------
set coeffs for one or more type pairs
------------------------------------------------------------------------- */
void PairBornCoulLong::coeff(int narg, char **arg)
{
if (narg < 7 || narg > 8) 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);
double a_one = force->numeric(arg[2]);
double rho_one = force->numeric(arg[3]);
double sigma_one = force->numeric(arg[4]);
if (rho_one <= 0) error->all(FLERR,"Incorrect args for pair coefficients");
double c_one = force->numeric(arg[5]);
double d_one = force->numeric(arg[6]);
double cut_lj_one = cut_lj_global;
if (narg == 8) cut_lj_one = force->numeric(arg[7]);
int count = 0;
for (int i = ilo; i <= ihi; i++) {
for (int j = MAX(jlo,i); j <= jhi; j++) {
a[i][j] = a_one;
rho[i][j] = rho_one;
sigma[i][j] = sigma_one;
c[i][j] = c_one;
d[i][j] = d_one;
cut_lj[i][j] = cut_lj_one;
setflag[i][j] = 1;
count++;
}
}
if (count == 0) error->all(FLERR,"Incorrect args for pair coefficients");
}
/* ----------------------------------------------------------------------
init for one type pair i,j and corresponding j,i
------------------------------------------------------------------------- */
double PairBornCoulLong::init_one(int i, int j)
{
if (setflag[i][j] == 0) error->all(FLERR,"All pair coeffs are not set");
double cut = MAX(cut_lj[i][j],cut_coul);
cut_ljsq[i][j] = cut_lj[i][j] * cut_lj[i][j];
rhoinv[i][j] = 1.0/rho[i][j];
born1[i][j] = a[i][j]/rho[i][j];
born2[i][j] = 6.0*c[i][j];
born3[i][j] = 8.0*d[i][j];
if (offset_flag) {
double rexp = exp((sigma[i][j]-cut_lj[i][j])*rhoinv[i][j]);
offset[i][j] = a[i][j]*rexp - c[i][j]/pow(cut_lj[i][j],6.0) +
d[i][j]/pow(cut_lj[i][j],8.0);
} else offset[i][j] = 0.0;
cut_ljsq[j][i] = cut_ljsq[i][j];
a[j][i] = a[i][j];
c[j][i] = c[i][j];
d[j][i] = d[i][j];
rhoinv[j][i] = rhoinv[i][j];
sigma[j][i] = sigma[i][j];
born1[j][i] = born1[i][j];
born2[j][i] = born2[i][j];
born3[j][i] = born3[i][j];
offset[j][i] = offset[i][j];
// compute I,J contribution to long-range tail correction
// count total # of atoms of type I and J via Allreduce
if (tail_flag) {
int *type = atom->type;
int nlocal = atom->nlocal;
double count[2],all[2];
count[0] = count[1] = 0.0;
for (int k = 0; k < nlocal; k++) {
if (type[k] == i) count[0] += 1.0;
if (type[k] == j) count[1] += 1.0;
}
MPI_Allreduce(count,all,2,MPI_DOUBLE,MPI_SUM,world);
double rho1 = rho[i][j];
double rho2 = rho1*rho1;
double rho3 = rho2*rho1;
double rc = cut_lj[i][j];
double rc2 = rc*rc;
double rc3 = rc2*rc;
double rc5 = rc3*rc2;
etail_ij = 2.0*MY_PI*all[0]*all[1] *
(a[i][j]*exp((sigma[i][j]-rc)/rho1)*rho1*
(rc2 + 2.0*rho1*rc + 2.0*rho2) -
c[i][j]/(3.0*rc3) + d[i][j]/(5.0*rc5));
ptail_ij = (-1/3.0)*2.0*MY_PI*all[0]*all[1] *
(-a[i][j]*exp((sigma[i][j]-rc)/rho1) *
(rc3 + 3.0*rho1*rc2 + 6.0*rho2*rc + 6.0*rho3) +
2.0*c[i][j]/rc3 - 8.0*d[i][j]/(5.0*rc5));
}
return cut;
}
/* ----------------------------------------------------------------------
init specific to this pair style
------------------------------------------------------------------------- */
void PairBornCoulLong::init_style()
{
if (!atom->q_flag)
error->all(FLERR,"Pair style born/coul/long requires atom attribute q");
cut_coulsq = cut_coul * cut_coul;
// insure use of KSpace long-range solver, set g_ewald
if (force->kspace == NULL)
error->all(FLERR,"Pair style requires a KSpace style");
g_ewald = force->kspace->g_ewald;
neighbor->request(this);
// setup force tables
if (ncoultablebits) init_tables(cut_coul,cut_respa);
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void PairBornCoulLong::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);
if (setflag[i][j]) {
fwrite(&a[i][j],sizeof(double),1,fp);
fwrite(&rho[i][j],sizeof(double),1,fp);
fwrite(&sigma[i][j],sizeof(double),1,fp);
fwrite(&c[i][j],sizeof(double),1,fp);
fwrite(&d[i][j],sizeof(double),1,fp);
fwrite(&cut_lj[i][j],sizeof(double),1,fp);
}
}
}
/* ----------------------------------------------------------------------
proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */
void PairBornCoulLong::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);
if (setflag[i][j]) {
if (me == 0) {
fread(&a[i][j],sizeof(double),1,fp);
fread(&rho[i][j],sizeof(double),1,fp);
fread(&sigma[i][j],sizeof(double),1,fp);
fread(&c[i][j],sizeof(double),1,fp);
fread(&d[i][j],sizeof(double),1,fp);
fread(&cut_lj[i][j],sizeof(double),1,fp);
}
MPI_Bcast(&a[i][j],1,MPI_DOUBLE,0,world);
MPI_Bcast(&rho[i][j],1,MPI_DOUBLE,0,world);
MPI_Bcast(&sigma[i][j],1,MPI_DOUBLE,0,world);
MPI_Bcast(&c[i][j],1,MPI_DOUBLE,0,world);
MPI_Bcast(&d[i][j],1,MPI_DOUBLE,0,world);
MPI_Bcast(&cut_lj[i][j],1,MPI_DOUBLE,0,world);
}
}
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void PairBornCoulLong::write_restart_settings(FILE *fp)
{
fwrite(&cut_lj_global,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);
fwrite(&tail_flag,sizeof(int),1,fp);
fwrite(&ncoultablebits,sizeof(int),1,fp);
fwrite(&tabinner,sizeof(double),1,fp);
}
/* ----------------------------------------------------------------------
proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */
void PairBornCoulLong::read_restart_settings(FILE *fp)
{
if (comm->me == 0) {
fread(&cut_lj_global,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);
fread(&tail_flag,sizeof(int),1,fp);
fread(&ncoultablebits,sizeof(int),1,fp);
fread(&tabinner,sizeof(double),1,fp);
}
MPI_Bcast(&cut_lj_global,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);
MPI_Bcast(&tail_flag,1,MPI_INT,0,world);
MPI_Bcast(&ncoultablebits,1,MPI_INT,0,world);
MPI_Bcast(&tabinner,1,MPI_DOUBLE,0,world);
}
/* ---------------------------------------------------------------------- */
double PairBornCoulLong::single(int i, int j, int itype, int jtype,
double rsq,
double factor_coul, double factor_lj,
double &fforce)
{
double r2inv,r6inv,r,rexp,grij,expm2,t,erfc,prefactor;
double fraction,table,forcecoul,forceborn,phicoul,phiborn;
int itable;
r2inv = 1.0/rsq;
if (rsq < cut_coulsq) {
if (!ncoultablebits || rsq <= tabinnersq) {
r = sqrt(rsq);
grij = g_ewald * r;
expm2 = exp(-grij*grij);
t = 1.0 / (1.0 + EWALD_P*grij);
erfc = t * (A1+t*(A2+t*(A3+t*(A4+t*A5)))) * expm2;
prefactor = force->qqrd2e * atom->q[i]*atom->q[j]/r;
forcecoul = prefactor * (erfc + EWALD_F*grij*expm2);
if (factor_coul < 1.0) forcecoul -= (1.0-factor_coul)*prefactor;
} else {
union_int_float_t rsq_lookup;
rsq_lookup.f = rsq;
itable = rsq_lookup.i & ncoulmask;
itable >>= ncoulshiftbits;
fraction = (rsq_lookup.f - rtable[itable]) * drtable[itable];
table = ftable[itable] + fraction*dftable[itable];
forcecoul = atom->q[i]*atom->q[j] * table;
if (factor_coul < 1.0) {
table = ctable[itable] + fraction*dctable[itable];
prefactor = atom->q[i]*atom->q[j] * table;
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((sigma[itype][jtype]-r)*rhoinv[itype][jtype]);
forceborn = born1[itype][jtype]*r*rexp - born2[itype][jtype]*r6inv +
born3[itype][jtype]*r2inv*r6inv;
} else forceborn = 0.0;
fforce = (forcecoul + factor_lj*forceborn) * r2inv;
double eng = 0.0;
if (rsq < cut_coulsq) {
if (!ncoultablebits || rsq <= tabinnersq)
phicoul = prefactor*erfc;
else {
table = etable[itable] + fraction*detable[itable];
phicoul = atom->q[i]*atom->q[j] * table;
}
if (factor_coul < 1.0) phicoul -= (1.0-factor_coul)*prefactor;
eng += phicoul;
}
if (rsq < cut_ljsq[itype][jtype]) {
phiborn = a[itype][jtype]*rexp - c[itype][jtype]*r6inv +
d[itype][jtype]*r2inv*r6inv - offset[itype][jtype];
eng += factor_lj*phiborn;
}
return eng;
}
/* ---------------------------------------------------------------------- */
void *PairBornCoulLong::extract(const char *str, int &dim)
{
dim = 0;
if (strcmp(str,"cut_coul") == 0) return (void *) &cut_coul;
return NULL;
}

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