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bond_nonlinear.cpp
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Sun, Apr 27, 23:26

bond_nonlinear.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
www.cs.sandia.gov/~sjplimp/lammps.html
Steve Plimpton, sjplimp@sandia.gov, Sandia National Laboratories
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 "bond_nonlinear.h"
#include "atom.h"
#include "neighbor.h"
#include "domain.h"
#include "comm.h"
#include "force.h"
#include "memory.h"
#include "error.h"
/* ----------------------------------------------------------------------
free all arrays
------------------------------------------------------------------------- */
BondNonlinear::~BondNonlinear()
{
if (allocated) {
memory->sfree(setflag);
memory->sfree(epsilon);
memory->sfree(r0);
memory->sfree(lamda);
}
}
/* ---------------------------------------------------------------------- */
void BondNonlinear::compute(int eflag, int vflag)
{
int i1,i2,n,type,factor;
double delx,dely,delz,rsq,r,dr,drsq,lamdasq,denom,denomsq,fforce,rfactor;
energy = 0.0;
if (vflag) for (n = 0; n < 6; n++) virial[n] = 0.0;
double **x = atom->x;
double **f = atom->f;
int **bondlist = neighbor->bondlist;
int nbondlist = neighbor->nbondlist;
int nlocal = atom->nlocal;
int newton_bond = force->newton_bond;
for (n = 0; n < nbondlist; n++) {
i1 = bondlist[n][0];
i2 = bondlist[n][1];
type = bondlist[n][2];
if (newton_bond) factor = 2;
else {
factor = 0;
if (i1 < nlocal) factor++;
if (i2 < nlocal) factor++;
}
rfactor = 0.5 * factor;
delx = x[i1][0] - x[i2][0];
dely = x[i1][1] - x[i2][1];
delz = x[i1][2] - x[i2][2];
domain->minimum_image(&delx,&dely,&delz);
rsq = delx*delx + dely*dely + delz*delz;
r = sqrt(rsq);
dr = r - r0[type];
drsq = dr*dr;
lamdasq = lamda[type]*lamda[type];
denom = lamdasq - drsq;
denomsq = denom*denom;
// force & energy
fforce = -epsilon[type]/r * 2.0*dr*lamdasq/denomsq;
if (eflag) energy += rfactor * epsilon[type] * drsq / denom;
// apply force to each of 2 atoms
if (newton_bond || i1 < nlocal) {
f[i1][0] += delx*fforce;
f[i1][1] += dely*fforce;
f[i1][2] += delz*fforce;
}
if (newton_bond || i2 < nlocal) {
f[i2][0] -= delx*fforce;
f[i2][1] -= dely*fforce;
f[i2][2] -= delz*fforce;
}
// virial contribution
if (vflag) {
virial[0] += rfactor*delx*delx*fforce;
virial[1] += rfactor*dely*dely*fforce;
virial[2] += rfactor*delz*delz*fforce;
virial[3] += rfactor*delx*dely*fforce;
virial[4] += rfactor*delx*delz*fforce;
virial[5] += rfactor*dely*delz*fforce;
}
}
}
/* ---------------------------------------------------------------------- */
void BondNonlinear::allocate()
{
allocated = 1;
int n = atom->nbondtypes;
epsilon = (double *) memory->smalloc((n+1)*sizeof(double),"bond:epsilon");
r0 = (double *) memory->smalloc((n+1)*sizeof(double),"bond:r0");
lamda = (double *) memory->smalloc((n+1)*sizeof(double),"bond:lamda");
setflag = (int *) memory->smalloc((n+1)*sizeof(int),"bond:setflag");
for (int i = 1; i <= n; i++) setflag[i] = 0;
}
/* ----------------------------------------------------------------------
set coeffs for one type
------------------------------------------------------------------------- */
void BondNonlinear::coeff(int narg, char **arg)
{
if (narg != 4) error->all("Incorrect args for bond coefficients");
if (!allocated) allocate();
int ilo,ihi;
force->bounds(arg[0],atom->nbondtypes,ilo,ihi);
double epsilon_one = atof(arg[1]);
double r0_one = atof(arg[2]);
double lamda_one = atof(arg[3]);
int count = 0;
for (int i = ilo; i <= ihi; i++) {
epsilon[i] = epsilon_one;
r0[i] = r0_one;
lamda[i] = lamda_one;
setflag[i] = 1;
count++;
}
if (count == 0) error->all("Incorrect args for bond coefficients");
}
/* ---------------------------------------------------------------------- */
double BondNonlinear::equilibrium_distance(int i)
{
return r0[i];
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void BondNonlinear::write_restart(FILE *fp)
{
fwrite(&epsilon[1],sizeof(double),atom->nbondtypes,fp);
fwrite(&r0[1],sizeof(double),atom->nbondtypes,fp);
fwrite(&lamda[1],sizeof(double),atom->nbondtypes,fp);
}
/* ----------------------------------------------------------------------
proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */
void BondNonlinear::read_restart(FILE *fp)
{
allocate();
if (comm->me == 0) {
fread(&epsilon[1],sizeof(double),atom->nbondtypes,fp);
fread(&r0[1],sizeof(double),atom->nbondtypes,fp);
fread(&lamda[1],sizeof(double),atom->nbondtypes,fp);
}
MPI_Bcast(&epsilon[1],atom->nbondtypes,MPI_DOUBLE,0,world);
MPI_Bcast(&r0[1],atom->nbondtypes,MPI_DOUBLE,0,world);
MPI_Bcast(&lamda[1],atom->nbondtypes,MPI_DOUBLE,0,world);
for (int i = 1; i <= atom->nbondtypes; i++) setflag[i] = 1;
}
/* ---------------------------------------------------------------------- */
void BondNonlinear::single(int type, double rsq, int i, int j, double rfactor,
int eflag, double &fforce, double &eng)
{
double r = sqrt(rsq);
double dr = r - r0[type];
double drsq = dr*dr;
double lamdasq = lamda[type]*lamda[type];
double denom = lamdasq - drsq;
double denomsq = denom*denom;
// force & energy
fforce = -epsilon[type]/r * 2.0*dr*lamdasq/denomsq;
if (eflag) eng = rfactor * epsilon[type] * drsq / denom;
}

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