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fix_nve.cpp
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Wed, Jun 5, 04:56

fix_nve.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.
------------------------------------------------------------------------- */
#include "stdio.h"
#include "string.h"
#include "fix_nve.h"
#include "atom.h"
#include "force.h"
#include "update.h"
#include "respa.h"
#include "error.h"
using namespace LAMMPS_NS;
/* ---------------------------------------------------------------------- */
FixNVE::FixNVE(LAMMPS *lmp, int narg, char **arg) :
Fix(lmp, narg, arg)
{
if (strcmp(style,"nve/sphere") != 0 && narg < 3)
error->all("Illegal fix nve command");
time_integrate = 1;
}
/* ---------------------------------------------------------------------- */
int FixNVE::setmask()
{
int mask = 0;
mask |= INITIAL_INTEGRATE;
mask |= FINAL_INTEGRATE;
mask |= INITIAL_INTEGRATE_RESPA;
mask |= FINAL_INTEGRATE_RESPA;
return mask;
}
/* ---------------------------------------------------------------------- */
void FixNVE::init()
{
dtv = update->dt;
dtf = 0.5 * update->dt * force->ftm2v;
if (strcmp(update->integrate_style,"respa") == 0)
step_respa = ((Respa *) update->integrate)->step;
}
/* ----------------------------------------------------------------------
allow for both per-type and per-atom mass
------------------------------------------------------------------------- */
void FixNVE::initial_integrate(int vflag)
{
double dtfm;
double **x = atom->x;
double **v = atom->v;
double **f = atom->f;
double *mass = atom->mass;
double *rmass = atom->rmass;
int *type = atom->type;
int *mask = atom->mask;
int nlocal = atom->nlocal;
if (igroup == atom->firstgroup) nlocal = atom->nfirst;
if (rmass) {
for (int i = 0; i < nlocal; i++) {
if (mask[i] & groupbit) {
dtfm = dtf / rmass[i];
v[i][0] += dtfm * f[i][0];
v[i][1] += dtfm * f[i][1];
v[i][2] += dtfm * f[i][2];
x[i][0] += dtv * v[i][0];
x[i][1] += dtv * v[i][1];
x[i][2] += dtv * v[i][2];
}
}
} else {
for (int i = 0; i < nlocal; i++) {
if (mask[i] & groupbit) {
dtfm = dtf / mass[type[i]];
v[i][0] += dtfm * f[i][0];
v[i][1] += dtfm * f[i][1];
v[i][2] += dtfm * f[i][2];
x[i][0] += dtv * v[i][0];
x[i][1] += dtv * v[i][1];
x[i][2] += dtv * v[i][2];
}
}
}
}
/* ---------------------------------------------------------------------- */
void FixNVE::final_integrate()
{
double dtfm;
double **v = atom->v;
double **f = atom->f;
double *mass = atom->mass;
double *rmass = atom->rmass;
int *type = atom->type;
int *mask = atom->mask;
int nlocal = atom->nlocal;
if (igroup == atom->firstgroup) nlocal = atom->nfirst;
if (rmass) {
for (int i = 0; i < nlocal; i++) {
if (mask[i] & groupbit) {
dtfm = dtf / rmass[i];
v[i][0] += dtfm * f[i][0];
v[i][1] += dtfm * f[i][1];
v[i][2] += dtfm * f[i][2];
}
}
} else {
for (int i = 0; i < nlocal; i++) {
if (mask[i] & groupbit) {
dtfm = dtf / mass[type[i]];
v[i][0] += dtfm * f[i][0];
v[i][1] += dtfm * f[i][1];
v[i][2] += dtfm * f[i][2];
}
}
}
}
/* ---------------------------------------------------------------------- */
void FixNVE::initial_integrate_respa(int vflag, int ilevel, int flag)
{
if (flag) return; // only used by NPT,NPH
dtv = step_respa[ilevel];
dtf = 0.5 * step_respa[ilevel] * force->ftm2v;
// innermost level - NVE update of v and x
// all other levels - NVE update of v
if (ilevel == 0) initial_integrate(vflag);
else final_integrate();
}
/* ---------------------------------------------------------------------- */
void FixNVE::final_integrate_respa(int ilevel)
{
dtf = 0.5 * step_respa[ilevel] * force->ftm2v;
final_integrate();
}
/* ---------------------------------------------------------------------- */
void FixNVE::reset_dt()
{
dtv = update->dt;
dtf = 0.5 * update->dt * force->ftm2v;
}

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