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lammps/src/pair_lj_cut_coul_long_tip4p.cpp
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pair_lj_cut_coul_long_tip4p.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
www.cs.sandia.gov/~sjplimp/lammps.html
Steve Plimpton, sjplimp@sandia.gov, Sandia National Laboratories
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 authors: Amalie Frischknecht and Ahmed Ismail (SNL)
------------------------------------------------------------------------- */
#include "math.h"
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "pair_lj_cut_coul_long_tip4p.h"
#include "angle.h"
#include "atom.h"
#include "bond.h"
#include "comm.h"
#include "domain.h"
#include "force.h"
#include "kspace.h"
#include "update.h"
#include "respa.h"
#include "memory.h"
#include "neighbor.h"
#include "error.h"
#define MIN(a,b) ((a) < (b) ? (a) : (b))
#define MAX(a,b) ((a) > (b) ? (a) : (b))
#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
/* ---------------------------------------------------------------------- */
PairLJCutCoulLongTIP4P::PairLJCutCoulLongTIP4P()
{
single_enable = 0;
}
/* ---------------------------------------------------------------------- */
void PairLJCutCoulLongTIP4P::compute(int eflag, int vflag)
{
int i,j,k,numneigh,itype,jtype,itable;
double qtmp,xtmp,ytmp,ztmp,delx,dely,delz,fraction,table;
double delx1,dely1,delz1,delx2,dely2,delz2,delx3,dely3,delz3;
double r,r2inv,r6inv,forcecoul,forcelj,cforce,negforce;
double factor_coul,factor_lj;
double grij,expm2,prefactor,t,erfc;
double phicoul,philj;
int iH1,iH2,jH1,jH2;
double xiM[3],xjM[3];
double *x1,*x2;
double fO[3],fH[3];
int *neighs;
double **f;
float rsq;
int *int_rsq = (int *) &rsq;
eng_vdwl = eng_coul = 0.0;
if (vflag) for (i = 0; i < 6; i++) virial[i] = tvirial[i] = 0.0;
if (vflag == 2) {
f = update->f_pair;
tf = atom->f;
}
else f = atom->f;
double **x = atom->x;
double *q = atom->q;
int *type = atom->type;
int nlocal = atom->nlocal;
int nall = atom->nlocal + atom->nghost;
double *special_coul = force->special_coul;
double *special_lj = force->special_lj;
double qqrd2e = force->qqrd2e;
// loop over neighbors of my atoms
for (i = 0; i < nlocal; i++) {
qtmp = q[i];
xtmp = x[i][0];
ytmp = x[i][1];
ztmp = x[i][2];
itype = type[i];
if (itype == typeO) {
find_M(i,iH1,iH2,xiM);
x1 = xiM;
} else x1 = x[i];
neighs = neighbor->firstneigh[i];
numneigh = neighbor->numneigh[i];
for (k = 0; k < numneigh; k++) {
j = neighs[k];
if (j < nall) factor_coul = factor_lj = 1.0;
else {
factor_coul = special_coul[j/nall];
factor_lj = special_lj[j/nall];
j %= nall;
}
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_ljsq[itype][jtype]) {
r6inv = r2inv*r2inv*r2inv;
forcelj = r6inv * (lj1[itype][jtype]*r6inv - lj2[itype][jtype]);
forcelj *= factor_lj * r2inv;
f[i][0] += delx*forcelj;
f[i][1] += dely*forcelj;
f[i][2] += delz*forcelj;
f[j][0] -= delx*forcelj;
f[j][1] -= dely*forcelj;
f[j][2] -= delz*forcelj;
if (eflag) {
philj = r6inv*(lj3[itype][jtype]*r6inv-lj4[itype][jtype]) -
offset[itype][jtype];
eng_vdwl += factor_lj*philj;
}
}
// adjust rsq for off-site O charge(s)
if (itype == typeO || jtype == typeO) {
if (jtype == typeO) {
find_M(j,jH1,jH2,xjM);
x2 = xjM;
} else x2 = x[j];
delx = x1[0] - x2[0];
dely = x1[1] - x2[1];
delz = x1[2] - x2[2];
rsq = delx*delx + dely*dely + delz*delz;
}
// test current rsq against cutoff and compute Coulombic force
if (rsq < cut_coulsq) {
if (!ncoultablebits || rsq <= tabinnersq) {
r = sqrtf(rsq);
r2inv = 1 / 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 {
r2inv = 1 / rsq;
itable = *int_rsq & ncoulmask;
itable >>= ncoulshiftbits;
fraction = (rsq - 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;
}
}
cforce = forcecoul * r2inv;
// if i,j are not O atoms, force is applied directly
// if i or j are O atoms, force is on fictitious atoms
// spread force to all 3 atoms in water molecule
// formulas due to Feenstra et al, J Comp Chem, 20, 786 (1999)
if (itype != typeO) {
if (vflag == 0) {
f[i][0] += delx * cforce;
f[i][1] += dely * cforce;
f[i][2] += delz * cforce;
} else {
tf[i][0] += delx * cforce;
tf[i][1] += dely * cforce;
tf[i][2] += delz * cforce;
tvirial[0] += 0.5 * delx * delx * cforce;
tvirial[1] += 0.5 * dely * dely * cforce;
tvirial[2] += 0.5 * delz * delz * cforce;
tvirial[3] += 0.5 * dely * delx * cforce;
tvirial[4] += 0.5 * delz * delx * cforce;
tvirial[5] += 0.5 * delz * dely * cforce;
}
} else {
fO[0] = delx*cforce*(1.0-2.0*alpha);
fO[1] = dely*cforce*(1.0-2.0*alpha);
fO[2] = delz*cforce*(1.0-2.0*alpha);
fH[0] = alpha * (delx*cforce);
fH[1] = alpha * (dely*cforce);
fH[2] = alpha * (delz*cforce);
if (vflag == 0) {
f[i][0] += fO[0];
f[i][1] += fO[1];
f[i][2] += fO[2];
f[iH1][0] += fH[0];
f[iH1][1] += fH[1];
f[iH1][2] += fH[2];
f[iH2][0] += fH[0];
f[iH2][1] += fH[1];
f[iH2][2] += fH[2];
} else {
tf[i][0] += fO[0];
tf[i][1] += fO[1];
tf[i][2] += fO[2];
tf[iH1][0] += fH[0];
tf[iH1][1] += fH[1];
tf[iH1][2] += fH[2];
tf[iH2][0] += fH[0];
tf[iH2][1] += fH[1];
tf[iH2][2] += fH[2];
delx1 = x[i][0] - x2[0];
dely1 = x[i][1] - x2[1];
delz1 = x[i][2] - x2[2];
domain->minimum_image(&delx1,&dely1,&delz1);
delx2 = x[iH1][0] - x2[0];
dely2 = x[iH1][1] - x2[1];
delz2 = x[iH1][2] - x2[2];
domain->minimum_image(&delx2,&dely2,&delz2);
delx3 = x[iH2][0] - x2[0];
dely3 = x[iH2][1] - x2[1];
delz3 = x[iH2][2] - x2[2];
domain->minimum_image(&delx3,&dely3,&delz3);
tvirial[0] += 0.5 * (delx1 * fO[0] + (delx2 + delx3) * fH[0]);
tvirial[1] += 0.5 * (dely1 * fO[1] + (dely2 + dely3) * fH[1]);
tvirial[2] += 0.5 * (delz1 * fO[2] + (delz2 + delz3) * fH[2]);
tvirial[3] += 0.5 * (dely1 * fO[0] + (dely2 + dely3) * fH[0]);
tvirial[4] += 0.5 * (delz1 * fO[0] + (delz2 + delz3) * fH[0]);
tvirial[5] += 0.5 * (delz1 * fO[1] + (delz2 + delz3) * fH[1]);
}
}
if (jtype != typeO) {
if (vflag == 0) {
f[j][0] -= delx * cforce;
f[j][1] -= dely * cforce;
f[j][2] -= delz * cforce;
} else {
tf[j][0] -= delx * cforce;
tf[j][1] -= dely * cforce;
tf[j][2] -= delz * cforce;
tvirial[0] += 0.5 * (delx * delx * cforce);
tvirial[1] += 0.5 * (dely * dely * cforce);
tvirial[2] += 0.5 * (delz * delz * cforce);
tvirial[3] += 0.5 * (dely * delx * cforce);
tvirial[4] += 0.5 * (delz * delx * cforce);
tvirial[5] += 0.5 * (delz * dely * cforce);
}
} else {
negforce = -cforce;
fO[0] = delx*negforce*(1.0-2.0*alpha);
fO[1] = dely*negforce*(1.0-2.0*alpha);
fO[2] = delz*negforce*(1.0-2.0*alpha);
fH[0] = alpha * (delx*negforce);
fH[1] = alpha * (dely*negforce);
fH[2] = alpha * (delz*negforce);
if (vflag != 2) {
f[j][0] += fO[0];
f[j][1] += fO[1];
f[j][2] += fO[2];
f[jH1][0] += fH[0];
f[jH1][1] += fH[1];
f[jH1][2] += fH[2];
f[jH2][0] += fH[0];
f[jH2][1] += fH[1];
f[jH2][2] += fH[2];
} else {
tf[j][0] += fO[0];
tf[j][1] += fO[1];
tf[j][2] += fO[2];
tf[jH1][0] += fH[0];
tf[jH1][1] += fH[1];
tf[jH1][2] += fH[2];
tf[jH2][0] += fH[0];
tf[jH2][1] += fH[1];
tf[jH2][2] += fH[2];
delx1 = x[j][0] - x1[0];
dely1 = x[j][1] - x1[1];
delz1 = x[j][2] - x1[2];
domain->minimum_image(&delx1,&dely1,&delz1);
delx2 = x[jH1][0] - x1[0];
dely2 = x[jH1][1] - x1[1];
delz2 = x[jH1][2] - x1[2];
domain->minimum_image(&delx2,&dely2,&delz2);
delx3 = x[jH2][0] - x1[0];
dely3 = x[jH2][1] - x1[1];
delz3 = x[jH2][2] - x1[2];
domain->minimum_image(&delx3,&dely3,&delz3);
tvirial[0] += 0.5 * (delx1 * fO[0] + (delx2 + delx3) * fH[0]);
tvirial[1] += 0.5 * (dely1 * fO[1] + (dely2 + dely3) * fH[1]);
tvirial[2] += 0.5 * (delz1 * fO[2] + (delz2 + delz3) * fH[2]);
tvirial[3] += 0.5 * (dely1 * fO[0] + (dely2 + dely3) * fH[0]);
tvirial[4] += 0.5 * (delz1 * fO[0] + (delz2 + delz3) * fH[0]);
tvirial[5] += 0.5 * (delz1 * fO[1] + (delz2 + delz3) * fH[1]);
}
}
if (eflag) {
if (!ncoultablebits || rsq <= tabinnersq)
phicoul = prefactor*erfc;
else {
table = etable[itable] + fraction*detable[itable];
phicoul = qtmp*q[j] * table;
}
if (factor_coul < 1.0) phicoul -= (1.0-factor_coul)*prefactor;
eng_coul += phicoul;
}
}
}
}
}
if (vflag == 2) {
virial_compute();
for (int i = 0; i < 6; i++) virial[i] += tvirial[i];
}
}
/* ----------------------------------------------------------------------
global settings
------------------------------------------------------------------------- */
void PairLJCutCoulLongTIP4P::settings(int narg, char **arg)
{
if (narg < 6 || narg > 7) error->all("Illegal pair_style command");
typeO = atoi(arg[0]);
typeH = atoi(arg[1]);
typeB = atoi(arg[2]);
typeA = atoi(arg[3]);
qdist = atof(arg[4]);
cut_lj_global = atof(arg[5]);
if (narg == 6) cut_coul = cut_lj_global;
else cut_coul = atof(arg[6]);
// 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;
}
}
/* ----------------------------------------------------------------------
init specific to this pair style
------------------------------------------------------------------------- */
void PairLJCutCoulLongTIP4P::init_style()
{
int i,j;
if (atom->tag_enable == 0)
error->all("Pair style lj/cut/coul/long/tip4p requires atom IDs");
if (!force->newton_pair)
error->all("Pair style lj/cut/coul/long/tip4p requires newton pair on");
if (atom->charge_allow == 0)
error->all("Must use charged atom style with this pair style");
cut_coulsq = cut_coul * cut_coul;
// set & error check interior rRESPA cutoffs
if (strcmp(update->integrate_style,"respa") == 0) {
if (((Respa *) update->integrate)->level_inner >= 0) {
cut_respa = ((Respa *) update->integrate)->cutoff;
for (i = 1; i <= atom->ntypes; i++)
for (j = i; j <= atom->ntypes; j++)
if (MIN(cut_lj[i][j],cut_coul) < cut_respa[3])
error->all("Pair cutoff < Respa interior cutoff");
}
} else cut_respa = NULL;
// insure use of correct KSpace long-range solver, set g_ewald
if (force->kspace == NULL)
error->all("Pair style is incompatible with KSpace style");
if (strcmp(force->kspace_style,"pppm/tip4p") == 0)
g_ewald = force->kspace->g_ewald;
else error->all("Pair style is incompatible with KSpace style");
// setup force tables
if (ncoultablebits) init_tables();
// set alpha parameter
double theta = force->angle->equilibrium_angle(typeA);
double blen = force->bond->equilibrium_distance(typeB);
alpha = qdist / (2.0 * cos(0.5*theta) * blen);
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void PairLJCutCoulLongTIP4P::write_restart_settings(FILE *fp)
{
fwrite(&typeO,sizeof(int),1,fp);
fwrite(&typeH,sizeof(int),1,fp);
fwrite(&typeB,sizeof(int),1,fp);
fwrite(&typeA,sizeof(int),1,fp);
fwrite(&qdist,sizeof(double),1,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);
}
/* ----------------------------------------------------------------------
proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */
void PairLJCutCoulLongTIP4P::read_restart_settings(FILE *fp)
{
if (comm->me == 0) {
fread(&typeO,sizeof(int),1,fp);
fread(&typeH,sizeof(int),1,fp);
fread(&typeB,sizeof(int),1,fp);
fread(&typeA,sizeof(int),1,fp);
fread(&qdist,sizeof(double),1,fp);
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);
}
MPI_Bcast(&typeO,1,MPI_INT,0,world);
MPI_Bcast(&typeH,1,MPI_INT,0,world);
MPI_Bcast(&typeB,1,MPI_INT,0,world);
MPI_Bcast(&typeA,1,MPI_INT,0,world);
MPI_Bcast(&qdist,1,MPI_DOUBLE,0,world);
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);
}
/* ----------------------------------------------------------------------
find 2 H atoms bonded to O atom i
compute position xM of fictitious charge site for O atom
also return local indices iH1,iH2 of H atoms
------------------------------------------------------------------------- */
void PairLJCutCoulLongTIP4P::find_M(int i, int &iH1, int &iH2, double *xM)
{
// test that O is correctly bonded to 2 succesive H atoms
iH1 = atom->map(atom->tag[i] + 1);
iH2 = atom->map(atom->tag[i] + 2);
if (iH1 == -1 || iH2 == -1) error->one("TIP4P hydrogen is missing");
if (atom->type[iH1] != typeH || atom->type[iH2] != typeH)
error->one("TIP4P hydrogen has incorrect atom type");
double **x = atom->x;
double delx1 = x[iH1][0] - x[i][0];
double dely1 = x[iH1][1] - x[i][1];
double delz1 = x[iH1][2] - x[i][2];
domain->minimum_image(&delx1,&dely1,&delz1);
double delx2 = x[iH2][0] - x[i][0];
double dely2 = x[iH2][1] - x[i][1];
double delz2 = x[iH2][2] - x[i][2];
domain->minimum_image(&delx2,&dely2,&delz2);
xM[0] = x[i][0] + alpha * (delx1 + delx2);
xM[1] = x[i][1] + alpha * (dely1 + dely2);
xM[2] = x[i][2] + alpha * (delz1 + delz2);
}
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