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fix_drag.cpp
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Sat, Jul 13, 06:34

fix_drag.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 "math.h"
#include "stdlib.h"
#include "string.h"
#include "fix_drag.h"
#include "atom.h"
#include "update.h"
#include "respa.h"
#include "domain.h"
#include "error.h"
using namespace LAMMPS_NS;
/* ---------------------------------------------------------------------- */
FixDrag::FixDrag(LAMMPS *lmp, int narg, char **arg) :
Fix(lmp, narg, arg)
{
if (narg != 8) error->all("Illegal fix drag command");
xflag = yflag = zflag = 1;
if (strcmp(arg[3],"NULL") == 0) xflag = 0;
else xc = atof(arg[3]);
if (strcmp(arg[4],"NULL") == 0) yflag = 0;
else yc = atof(arg[4]);
if (strcmp(arg[5],"NULL") == 0) zflag = 0;
else zc = atof(arg[5]);
f_mag = atof(arg[6]);
delta = atof(arg[7]);
}
/* ---------------------------------------------------------------------- */
int FixDrag::setmask()
{
int mask = 0;
mask |= POST_FORCE;
mask |= POST_FORCE_RESPA;
return mask;
}
/* ---------------------------------------------------------------------- */
void FixDrag::init()
{
if (strcmp(update->integrate_style,"respa") == 0)
nlevels_respa = ((Respa *) update->integrate)->nlevels;
}
/* ---------------------------------------------------------------------- */
void FixDrag::setup()
{
if (strcmp(update->integrate_style,"verlet") == 0)
post_force(1);
else {
((Respa *) update->integrate)->copy_flevel_f(nlevels_respa-1);
post_force_respa(1,nlevels_respa-1,0);
((Respa *) update->integrate)->copy_f_flevel(nlevels_respa-1);
}
}
/* ---------------------------------------------------------------------- */
void FixDrag::post_force(int vflag)
{
// apply drag force to atoms in group of magnitude f_mag
// apply in direction (r-r0) if atom is further than delta away
double **x = atom->x;
double **f = atom->f;
int *mask = atom->mask;
int nlocal = atom->nlocal;
double dx,dy,dz,r,prefactor;
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
dx = x[i][0] - xc;
dy = x[i][1] - yc;
dz = x[i][2] - zc;
if (!xflag) dx = 0.0;
if (!yflag) dy = 0.0;
if (!zflag) dz = 0.0;
domain->minimum_image(&dx,&dy,&dz);
r = sqrt(dx*dx + dy*dy + dz*dz);
if (r > delta) {
prefactor = f_mag/r;
f[i][0] -= prefactor*dx;
f[i][1] -= prefactor*dy;
f[i][2] -= prefactor*dz;
}
}
}
/* ---------------------------------------------------------------------- */
void FixDrag::post_force_respa(int vflag, int ilevel, int iloop)
{
if (ilevel == nlevels_respa-1) post_force(vflag);
}

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