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fix_wall_lj1043.cpp
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Tue, Aug 6, 15:20

fix_wall_lj1043.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: Jonathan Lee (Sandia)
------------------------------------------------------------------------- */
#include <math.h>
#include "fix_wall_lj1043.h"
#include "atom.h"
#include "math_const.h"
using namespace LAMMPS_NS;
using namespace MathConst;
/* ---------------------------------------------------------------------- */
FixWallLJ1043::FixWallLJ1043(LAMMPS *lmp, int narg, char **arg) :
FixWall(lmp, narg, arg) {}
/* ---------------------------------------------------------------------- */
void FixWallLJ1043::precompute(int m)
{
coeff1[m] = MY_2PI * 2.0/5.0 * epsilon[m] * pow(sigma[m],10.0);
coeff2[m] = MY_2PI * epsilon[m] * pow(sigma[m],4.0);
coeff3[m] = MY_2PI * pow(2.0,1/2.0) / 3 * epsilon[m] * pow(sigma[m],3.0);
coeff4[m] = 0.61 / pow(2.0,1/2.0) * sigma[m];
coeff5[m] = coeff1[m] * 10.0;
coeff6[m] = coeff2[m] * 4.0;
coeff7[m] = coeff3[m] * 3.0;
double rinv = 1.0/cutoff[m];
double r2inv = rinv*rinv;
double r4inv = r2inv*r2inv;
offset[m] = coeff1[m]*r4inv*r4inv*r2inv - coeff2[m]*r4inv -
coeff3[m]*pow(cutoff[m]+coeff4[m],-3.0);
}
/* ---------------------------------------------------------------------- */
void FixWallLJ1043::wall_particle(int m, int which, double coord)
{
double delta,rinv,r2inv,r4inv,r10inv,fwall;
double **x = atom->x;
double **f = atom->f;
int *mask = atom->mask;
int nlocal = atom->nlocal;
int dim = which / 2;
int side = which % 2;
if (side == 0) side = -1;
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
if (side < 0) delta = x[i][dim] - coord;
else delta = coord - x[i][dim];
if (delta <= 0.0) continue;
if (delta > cutoff[m]) continue;
rinv = 1.0/delta;
r2inv = rinv*rinv;
r4inv = r2inv*r2inv;
r10inv = r4inv*r4inv*r2inv;
fwall = side * (coeff5[m]*r10inv*rinv - coeff6[m]*r4inv*rinv -
coeff7[m]*pow(delta+coeff4[m],-4.0));
f[i][dim] -= fwall;
ewall[0] += coeff1[m]*r10inv - coeff2[m]*r4inv -
coeff3[m]*pow(delta+coeff4[m],-3.0) - offset[m];
ewall[m+1] += fwall;
}
}

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