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fix_mvv_dpd.cpp
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Wed, May 22, 16:17

fix_mvv_dpd.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.
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
This is a time integrator for position and velocity (x and v) using the
modified velocity-Verlet (MVV) algorithm.
Setting verlet = 0.5 recovers the standard velocity-Verlet algorithm.
Contributing author: Zhen Li (Brown University)
Email: zhen_li@brown.edu
------------------------------------------------------------------------- */
#include <stdio.h>
#include <string.h>
#include "fix_mvv_dpd.h"
#include "atom.h"
#include "force.h"
#include "update.h"
#include "respa.h"
#include "error.h"
using namespace LAMMPS_NS;
using namespace FixConst;
/* ---------------------------------------------------------------------- */
FixMvvDPD::FixMvvDPD(LAMMPS *lmp, int narg, char **arg) :
Fix(lmp, narg, arg)
{
if (strcmp(style,"mvv/dpd") != 0 && narg < 3)
error->all(FLERR,"Illegal fix mvv/dpd command");
verlet = 0.5;
if(narg > 3) verlet = force->numeric(FLERR,arg[3]);
dynamic_group_allow = 1;
time_integrate = 1;
}
/* ---------------------------------------------------------------------- */
int FixMvvDPD::setmask()
{
int mask = 0;
mask |= INITIAL_INTEGRATE;
mask |= FINAL_INTEGRATE;
return mask;
}
/* ---------------------------------------------------------------------- */
void FixMvvDPD::init()
{
dtv = update->dt;
dtf = 0.5 * update->dt * force->ftm2v;
}
/* ----------------------------------------------------------------------
allow for both per-type and per-atom mass
------------------------------------------------------------------------- */
void FixMvvDPD::initial_integrate(int vflag)
{
double dtfm;
double **x = atom->x;
double **v = atom->v;
double **f = atom->f;
double **vest = atom->vest;
double *rmass = atom->rmass;
double *mass = atom->mass;
int *type = atom->type;
int *mask = atom->mask;
int nlocal = atom->nlocal;
if (igroup == atom->firstgroup) nlocal = atom->nfirst;
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
if (rmass) dtfm = dtf / rmass[i];
else dtfm = dtf / mass[type[i]];
vest[i][0] = v[i][0] + dtfm * f[i][0];
vest[i][1] = v[i][1] + dtfm * f[i][1];
vest[i][2] = v[i][2] + dtfm * f[i][2];
x[i][0] += dtv * vest[i][0];
x[i][1] += dtv * vest[i][1];
x[i][2] += dtv * vest[i][2];
v[i][0] += 2.0 * verlet * dtfm * f[i][0];
v[i][1] += 2.0 * verlet * dtfm * f[i][1];
v[i][2] += 2.0 * verlet * dtfm * f[i][2];
}
}
/* ---------------------------------------------------------------------- */
void FixMvvDPD::final_integrate()
{
double dtfm;
double **v = atom->v;
double **f = atom->f;
double **vest = atom->vest;
double *rmass = atom->rmass;
double *mass = atom->mass;
int *type = atom->type;
int *mask = atom->mask;
int nlocal = atom->nlocal;
if (igroup == atom->firstgroup) nlocal = atom->nfirst;
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
if (rmass) dtfm = dtf / rmass[i];
else dtfm = dtf / mass[type[i]];
v[i][0] = vest[i][0] + dtfm * f[i][0];
v[i][1] = vest[i][1] + dtfm * f[i][1];
v[i][2] = vest[i][2] + dtfm * f[i][2];
}
}
/* ---------------------------------------------------------------------- */
void FixMvvDPD::reset_dt()
{
dtv = update->dt;
dtf = 0.5 * update->dt * force->ftm2v;
}

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