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fix_wall_lj126.cpp
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Mon, Nov 11, 06:31

fix_wall_lj126.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 "fix_wall_lj126.h"
#include "atom.h"
#include "error.h"
using namespace LAMMPS_NS;
using namespace FixConst;
/* ---------------------------------------------------------------------- */
FixWallLJ126::FixWallLJ126(LAMMPS *lmp, int narg, char **arg) :
FixWall(lmp, narg, arg) {}
/* ---------------------------------------------------------------------- */
void FixWallLJ126::precompute(int m)
{
coeff1[m] = 48.0 * epsilon[m] * pow(sigma[m],12.0);
coeff2[m] = 24.0 * epsilon[m] * pow(sigma[m],6.0);
coeff3[m] = 4.0 * epsilon[m] * pow(sigma[m],12.0);
coeff4[m] = 4.0 * epsilon[m] * pow(sigma[m],6.0);
double r2inv = 1.0/(cutoff[m]*cutoff[m]);
double r6inv = r2inv*r2inv*r2inv;
offset[m] = r6inv*(coeff3[m]*r6inv - coeff4[m]);
}
/* ----------------------------------------------------------------------
interaction of all particles in group with a wall
m = index of wall coeffs
which = xlo,xhi,ylo,yhi,zlo,zhi
error if any particle is on or behind wall
------------------------------------------------------------------------- */
void FixWallLJ126::wall_particle(int m, int which, double coord)
{
double delta,rinv,r2inv,r6inv,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;
int onflag = 0;
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 >= cutoff[m]) continue;
if (delta <= 0.0) {
onflag = 1;
continue;
}
rinv = 1.0/delta;
r2inv = rinv*rinv;
r6inv = r2inv*r2inv*r2inv;
fwall = side * r6inv*(coeff1[m]*r6inv - coeff2[m]) * rinv;
f[i][dim] -= fwall;
ewall[0] += r6inv*(coeff3[m]*r6inv - coeff4[m]) - offset[m];
ewall[m+1] += fwall;
}
if (onflag) error->one(FLERR,"Particle on or inside fix wall surface");
}

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