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pair_dpd_conservative.cpp
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Mon, Nov 11, 06:47

pair_dpd_conservative.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: James Larentzos (U.S. Army Research Laboratory)
------------------------------------------------------------------------- */
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "pair_dpd_conservative.h"
#include "atom.h"
#include "atom_vec.h"
#include "comm.h"
#include "update.h"
#include "fix.h"
#include "force.h"
#include "neighbor.h"
#include "neigh_list.h"
#include "neigh_request.h"
#include "memory.h"
#include "modify.h"
#include "error.h"
using namespace LAMMPS_NS;
#define EPSILON 1.0e-10
/* ---------------------------------------------------------------------- */
PairDPDconservative::PairDPDconservative(LAMMPS *lmp) : Pair(lmp)
{
}
/* ---------------------------------------------------------------------- */
PairDPDconservative::~PairDPDconservative()
{
if (allocated) {
memory->destroy(setflag);
memory->destroy(cutsq);
memory->destroy(cut);
memory->destroy(a0);
}
}
/* ---------------------------------------------------------------------- */
void PairDPDconservative::compute(int eflag, int vflag)
{
int i,j,ii,jj,inum,jnum,itype,jtype;
double xtmp,ytmp,ztmp,delx,dely,delz,evdwl,fpair;
double rsq,r,rinv,wd,wr,factor_dpd;
int *ilist,*jlist,*numneigh,**firstneigh;
evdwl = 0.0;
if (eflag || vflag) ev_setup(eflag,vflag);
else evflag = vflag_fdotr = 0;
double **x = atom->x;
double **f = atom->f;
int *type = atom->type;
int nlocal = atom->nlocal;
double *special_lj = force->special_lj;
int newton_pair = force->newton_pair;
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];
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_dpd = special_lj[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]) {
r = sqrt(rsq);
if (r < EPSILON) continue; // r can be 0.0 in DPD systems
rinv = 1.0/r;
wr = 1.0 - r/cut[itype][jtype];
wd = wr*wr;
// conservative force = a0 * wr
fpair = a0[itype][jtype]*wr;
fpair *= factor_dpd*rinv;
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) {
// unshifted eng of conservative term:
// evdwl = -a0[itype][jtype]*r * (1.0-0.5*r/cut[itype][jtype]);
// eng shifted to 0.0 at cutoff
evdwl = 0.5*a0[itype][jtype]*cut[itype][jtype] * wd;
evdwl *= factor_dpd;
}
if (evflag) ev_tally(i,j,nlocal,newton_pair,
evdwl,0.0,fpair,delx,dely,delz);
}
}
}
if (vflag_fdotr) virial_fdotr_compute();
}
/* ----------------------------------------------------------------------
allocate all arrays
------------------------------------------------------------------------- */
void PairDPDconservative::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,n+1,n+1,"pair:cut");
memory->create(a0,n+1,n+1,"pair:a0");
}
/* ----------------------------------------------------------------------
global settings
------------------------------------------------------------------------- */
void PairDPDconservative::settings(int narg, char **arg)
{
// process keywords
if (narg != 1) error->all(FLERR,"Illegal pair_style command");
cut_global = force->numeric(FLERR,arg[0]);
// 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[i][j] = cut_global;
}
}
/* ----------------------------------------------------------------------
set coeffs for one or more type pairs
------------------------------------------------------------------------- */
void PairDPDconservative::coeff(int narg, char **arg)
{
if (narg < 3 || narg > 4) 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 a0_one = force->numeric(FLERR,arg[2]);
double cut_one = cut_global;
if (narg == 4) cut_one = force->numeric(FLERR,arg[3]);
int count = 0;
for (int i = ilo; i <= ihi; i++) {
for (int j = MAX(jlo,i); j <= jhi; j++) {
a0[i][j] = a0_one;
cut[i][j] = cut_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 PairDPDconservative::init_one(int i, int j)
{
if (setflag[i][j] == 0) error->all(FLERR,"All pair coeffs are not set");
cut[j][i] = cut[i][j];
a0[j][i] = a0[i][j];
return cut[i][j];
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void PairDPDconservative::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(&a0[i][j],sizeof(double),1,fp);
fwrite(&cut[i][j],sizeof(double),1,fp);
}
}
}
/* ----------------------------------------------------------------------
proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */
void PairDPDconservative::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(&a0[i][j],sizeof(double),1,fp);
fread(&cut[i][j],sizeof(double),1,fp);
}
MPI_Bcast(&a0[i][j],1,MPI_DOUBLE,0,world);
MPI_Bcast(&cut[i][j],1,MPI_DOUBLE,0,world);
}
}
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void PairDPDconservative::write_restart_settings(FILE *fp)
{
fwrite(&cut_global,sizeof(double),1,fp);
fwrite(&mix_flag,sizeof(int),1,fp);
}
/* ----------------------------------------------------------------------
proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */
void PairDPDconservative::read_restart_settings(FILE *fp)
{
if (comm->me == 0) {
fread(&cut_global,sizeof(double),1,fp);
fread(&mix_flag,sizeof(int),1,fp);
}
MPI_Bcast(&cut_global,1,MPI_DOUBLE,0,world);
MPI_Bcast(&mix_flag,1,MPI_INT,0,world);
}
/* ---------------------------------------------------------------------- */
double PairDPDconservative::single(int i, int j, int itype, int jtype, double rsq,
double factor_coul, double factor_dpd, double &fforce)
{
double r,rinv,wr,wd,phi;
r = sqrt(rsq);
if (r < EPSILON) {
fforce = 0.0;
return 0.0;
}
rinv = 1.0/r;
wr = 1.0 - r/cut[itype][jtype];
wd = wr*wr;
fforce = a0[itype][jtype]*wr * factor_dpd*rinv;
phi = 0.5*a0[itype][jtype]*cut[itype][jtype] * wd;
return factor_dpd*phi;
}

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