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fix_heat.cpp
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Sat, Jul 13, 01:37

fix_heat.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 "stdlib.h"
#include "string.h"
#include "fix_heat.h"
#include "atom.h"
#include "domain.h"
#include "group.h"
#include "force.h"
#include "update.h"
#include "error.h"
using namespace LAMMPS_NS;
/* ---------------------------------------------------------------------- */
FixHeat::FixHeat(LAMMPS *lmp, int narg, char **arg) : Fix(lmp, narg, arg)
{
if (narg < 4) error->all("Illegal fix heat command");
scalar_flag = 1;
global_freq = 1;
extscalar = 0;
nevery = atoi(arg[3]);
if (nevery <= 0) error->all("Illegal fix heat command");
heat_input = atof(arg[4]);
scale = 1.0;
}
/* ---------------------------------------------------------------------- */
int FixHeat::setmask()
{
int mask = 0;
mask |= END_OF_STEP;
return mask;
}
/* ---------------------------------------------------------------------- */
void FixHeat::init()
{
// cannot have 0 atoms in group
if (group->count(igroup) == 0.0) error->all("Fix heat group has no atoms");
masstotal = group->mass(igroup);
}
/* ---------------------------------------------------------------------- */
void FixHeat::end_of_step()
{
double **v = atom->v;
int *mask = atom->mask;
int nlocal = atom->nlocal;
double vsub[3],vcm[3];
double heat = heat_input*nevery*update->dt*force->ftm2v;
double ke = group->ke(igroup)*force->ftm2v;
group->vcm(igroup,masstotal,vcm);
double vcmsq = vcm[0]*vcm[0] + vcm[1]*vcm[1] + vcm[2]*vcm[2];
double escale = (ke + heat - 0.5*vcmsq*masstotal)/(ke - 0.5*vcmsq*masstotal);
if (escale < 0.0) error->all("Fix heat kinetic energy went negative");
scale = sqrt(escale);
vsub[0] = (scale-1.0) * vcm[0];
vsub[1] = (scale-1.0) * vcm[1];
vsub[2] = (scale-1.0) * vcm[2];
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
v[i][0] = scale*v[i][0] - vsub[0];
v[i][1] = scale*v[i][1] - vsub[1];
v[i][2] = scale*v[i][2] - vsub[2];
}
}
/* ---------------------------------------------------------------------- */
double FixHeat::compute_scalar()
{
return scale;
}

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