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rLAMMPS lammps
pair_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: Paul Crozier (SNL)
------------------------------------------------------------------------- */
#include "math.h"
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "pair_coul_long.h"
#include "atom.h"
#include "comm.h"
#include "force.h"
#include "kspace.h"
#include "neighbor.h"
#include "neigh_list.h"
#include "update.h"
#include "integrate.h"
#include "respa.h"
#include "memory.h"
#include "error.h"
using namespace LAMMPS_NS;
#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
/* ---------------------------------------------------------------------- */
PairCoulLong::PairCoulLong(LAMMPS *lmp) : Pair(lmp)
{
ftable = NULL;
}
/* ---------------------------------------------------------------------- */
PairCoulLong::~PairCoulLong()
{
if (allocated) {
memory->destroy(setflag);
memory->destroy(cutsq);
memory->destroy(scale);
}
if (ftable) free_tables();
}
/* ---------------------------------------------------------------------- */
void PairCoulLong::compute(int eflag, int vflag)
{
int i,j,ii,jj,inum,jnum,itable,itype,jtype;
double qtmp,xtmp,ytmp,ztmp,delx,dely,delz,ecoul,fpair;
double fraction,table;
double r,r2inv,forcecoul,factor_coul;
double grij,expm2,prefactor,t,erfc;
int *ilist,*jlist,*numneigh,**firstneigh;
double rsq;
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;
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_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 < cut_coulsq) {
r2inv = 1.0/rsq;
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 * scale[itype][jtype] * 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 = scale[itype][jtype] * qtmp*q[j] * table;
if (factor_coul < 1.0) {
table = ctable[itable] + fraction*dctable[itable];
prefactor = scale[itype][jtype] * qtmp*q[j] * table;
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) {
if (!ncoultablebits || rsq <= tabinnersq)
ecoul = prefactor*erfc;
else {
table = etable[itable] + fraction*detable[itable];
ecoul = scale[itype][jtype] * qtmp*q[j] * table;
}
if (factor_coul < 1.0) ecoul -= (1.0-factor_coul)*prefactor;
}
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 PairCoulLong::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(scale,n+1,n+1,"pair:scale");
}
/* ----------------------------------------------------------------------
global settings
------------------------------------------------------------------------- */
void PairCoulLong::settings(int narg, char **arg)
{
if (narg != 1) error->all(FLERR,"Illegal pair_style command");
cut_coul = force->numeric(arg[0]);
}
/* ----------------------------------------------------------------------
set coeffs for one or more type pairs
------------------------------------------------------------------------- */
void PairCoulLong::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++) {
scale[i][j] = 1.0;
setflag[i][j] = 1;
count++;
}
}
if (count == 0) error->all(FLERR,"Incorrect args for pair coefficients");
}
/* ----------------------------------------------------------------------
init specific to this pair style
------------------------------------------------------------------------- */
void PairCoulLong::init_style()
{
if (!atom->q_flag)
error->all(FLERR,"Pair style lj/cut/coul/long requires atom attribute q");
neighbor->request(this);
cut_coulsq = cut_coul * cut_coul;
// set & error check interior rRESPA cutoffs
if (strstr(update->integrate_style,"respa") &&
((Respa *) update->integrate)->level_inner >= 0) {
cut_respa = ((Respa *) update->integrate)->cutoff;
if (cut_coul < cut_respa[3])
error->all(FLERR,"Pair cutoff < Respa interior cutoff");
} else cut_respa = NULL;
// insure use of KSpace long-range solver, set g_ewald
if (force->kspace == NULL)
error->all(FLERR,"Pair style is incompatible with KSpace style");
g_ewald = force->kspace->g_ewald;
// setup force tables
if (ncoultablebits) init_tables();
}
/* ----------------------------------------------------------------------
init for one type pair i,j and corresponding j,i
------------------------------------------------------------------------- */
double PairCoulLong::init_one(int i, int j)
{
scale[j][i] = scale[i][j];
return cut_coul;
}
/* ----------------------------------------------------------------------
setup force tables used in compute routines
------------------------------------------------------------------------- */
void PairCoulLong::init_tables()
{
int masklo,maskhi;
double r,grij,expm2,derfc,rsw;
double qqrd2e = force->qqrd2e;
tabinnersq = tabinner*tabinner;
init_bitmap(tabinner,cut_coul,ncoultablebits,
masklo,maskhi,ncoulmask,ncoulshiftbits);
int ntable = 1;
for (int i = 0; i < ncoultablebits; i++) ntable *= 2;
// linear lookup tables of length N = 2^ncoultablebits
// stored value = value at lower edge of bin
// d values = delta from lower edge to upper edge of bin
if (ftable) free_tables();
memory->create(rtable,ntable,"pair:rtable");
memory->create(ftable,ntable,"pair:ftable");
memory->create(ctable,ntable,"pair:ctable");
memory->create(etable,ntable,"pair:etable");
memory->create(drtable,ntable,"pair:drtable");
memory->create(dftable,ntable,"pair:dftable");
memory->create(dctable,ntable,"pair:dctable");
memory->create(detable,ntable,"pair:detable");
if (cut_respa == NULL) {
vtable = ptable = dvtable = dptable = NULL;
} else {
memory->create(vtable,ntable,"pair:vtable");
memory->create(ptable,ntable,"pair:ptable");
memory->create(dvtable,ntable,"pair:dvtable");
memory->create(dptable,ntable,"pair:dptable");
}
union_int_float_t rsq_lookup;
union_int_float_t minrsq_lookup;
int itablemin;
minrsq_lookup.i = 0 << ncoulshiftbits;
minrsq_lookup.i |= maskhi;
for (int i = 0; i < ntable; i++) {
rsq_lookup.i = i << ncoulshiftbits;
rsq_lookup.i |= masklo;
if (rsq_lookup.f < tabinnersq) {
rsq_lookup.i = i << ncoulshiftbits;
rsq_lookup.i |= maskhi;
}
r = sqrtf(rsq_lookup.f);
grij = g_ewald * r;
expm2 = exp(-grij*grij);
derfc = erfc(grij);
if (cut_respa == NULL) {
rtable[i] = rsq_lookup.f;
ftable[i] = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
ctable[i] = qqrd2e/r;
etable[i] = qqrd2e/r * derfc;
} else {
rtable[i] = rsq_lookup.f;
ftable[i] = qqrd2e/r * (derfc + EWALD_F*grij*expm2 - 1.0);
ctable[i] = 0.0;
etable[i] = qqrd2e/r * derfc;
ptable[i] = qqrd2e/r;
vtable[i] = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
if (rsq_lookup.f > cut_respa[2]*cut_respa[2]) {
if (rsq_lookup.f < cut_respa[3]*cut_respa[3]) {
rsw = (r - cut_respa[2])/(cut_respa[3] - cut_respa[2]);
ftable[i] += qqrd2e/r * rsw*rsw*(3.0 - 2.0*rsw);
ctable[i] = qqrd2e/r * rsw*rsw*(3.0 - 2.0*rsw);
} else {
ftable[i] = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
ctable[i] = qqrd2e/r;
}
}
}
minrsq_lookup.f = MIN(minrsq_lookup.f,rsq_lookup.f);
}
tabinnersq = minrsq_lookup.f;
int ntablem1 = ntable - 1;
for (int i = 0; i < ntablem1; i++) {
drtable[i] = 1.0/(rtable[i+1] - rtable[i]);
dftable[i] = ftable[i+1] - ftable[i];
dctable[i] = ctable[i+1] - ctable[i];
detable[i] = etable[i+1] - etable[i];
}
if (cut_respa) {
for (int i = 0; i < ntablem1; i++) {
dvtable[i] = vtable[i+1] - vtable[i];
dptable[i] = ptable[i+1] - ptable[i];
}
}
// get the delta values for the last table entries
// tables are connected periodically between 0 and ntablem1
drtable[ntablem1] = 1.0/(rtable[0] - rtable[ntablem1]);
dftable[ntablem1] = ftable[0] - ftable[ntablem1];
dctable[ntablem1] = ctable[0] - ctable[ntablem1];
detable[ntablem1] = etable[0] - etable[ntablem1];
if (cut_respa) {
dvtable[ntablem1] = vtable[0] - vtable[ntablem1];
dptable[ntablem1] = ptable[0] - ptable[ntablem1];
}
// get the correct delta values at itablemax
// smallest r is in bin itablemin
// largest r is in bin itablemax, which is itablemin-1,
// or ntablem1 if itablemin=0
// deltas at itablemax only needed if corresponding rsq < cut*cut
// if so, compute deltas between rsq and cut*cut
double f_tmp,c_tmp,e_tmp,p_tmp,v_tmp;
itablemin = minrsq_lookup.i & ncoulmask;
itablemin >>= ncoulshiftbits;
int itablemax = itablemin - 1;
if (itablemin == 0) itablemax = ntablem1;
rsq_lookup.i = itablemax << ncoulshiftbits;
rsq_lookup.i |= maskhi;
if (rsq_lookup.f < cut_coulsq) {
rsq_lookup.f = cut_coulsq;
r = sqrtf(rsq_lookup.f);
grij = g_ewald * r;
expm2 = exp(-grij*grij);
derfc = erfc(grij);
if (cut_respa == NULL) {
f_tmp = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
c_tmp = qqrd2e/r;
e_tmp = qqrd2e/r * derfc;
} else {
f_tmp = qqrd2e/r * (derfc + EWALD_F*grij*expm2 - 1.0);
c_tmp = 0.0;
e_tmp = qqrd2e/r * derfc;
p_tmp = qqrd2e/r;
v_tmp = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
if (rsq_lookup.f > cut_respa[2]*cut_respa[2]) {
if (rsq_lookup.f < cut_respa[3]*cut_respa[3]) {
rsw = (r - cut_respa[2])/(cut_respa[3] - cut_respa[2]);
f_tmp += qqrd2e/r * rsw*rsw*(3.0 - 2.0*rsw);
c_tmp = qqrd2e/r * rsw*rsw*(3.0 - 2.0*rsw);
} else {
f_tmp = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
c_tmp = qqrd2e/r;
}
}
}
drtable[itablemax] = 1.0/(rsq_lookup.f - rtable[itablemax]);
dftable[itablemax] = f_tmp - ftable[itablemax];
dctable[itablemax] = c_tmp - ctable[itablemax];
detable[itablemax] = e_tmp - etable[itablemax];
if (cut_respa) {
dvtable[itablemax] = v_tmp - vtable[itablemax];
dptable[itablemax] = p_tmp - ptable[itablemax];
}
}
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void PairCoulLong::write_restart(FILE *fp)
{
write_restart_settings(fp);
}
/* ----------------------------------------------------------------------
proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */
void PairCoulLong::read_restart(FILE *fp)
{
read_restart_settings(fp);
allocate();
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void PairCoulLong::write_restart_settings(FILE *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 PairCoulLong::read_restart_settings(FILE *fp)
{
if (comm->me == 0) {
fread(&cut_coul,sizeof(double),1,fp);
fread(&offset_flag,sizeof(int),1,fp);
fread(&mix_flag,sizeof(int),1,fp);
}
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);
}
/* ----------------------------------------------------------------------
free memory for tables used in pair computations
------------------------------------------------------------------------- */
void PairCoulLong::free_tables()
{
memory->destroy(rtable);
memory->destroy(drtable);
memory->destroy(ftable);
memory->destroy(dftable);
memory->destroy(ctable);
memory->destroy(dctable);
memory->destroy(etable);
memory->destroy(detable);
memory->destroy(vtable);
memory->destroy(dvtable);
memory->destroy(ptable);
memory->destroy(dptable);
}
/* ---------------------------------------------------------------------- */
double PairCoulLong::single(int i, int j, int itype, int jtype,
double rsq,
double factor_coul, double factor_lj,
double &fforce)
{
double r2inv,r,grij,expm2,t,erfc,prefactor;
double fraction,table,forcecoul,phicoul;
int itable;
r2inv = 1.0/rsq;
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;
}
}
fforce = forcecoul * r2inv;
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;
return phicoul;
}
/* ---------------------------------------------------------------------- */
void *PairCoulLong::extract(char *str, int &dim)
{
if (strcmp(str,"cut_coul") == 0) {
dim = 0;
return (void *) &cut_coul;
}
if (strcmp(str,"scale") == 0) {
dim = 2;
return (void *) scale;
}
return NULL;
}
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