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bond_fene.cpp
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Sat, Nov 16, 21:05

bond_fene.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 "lmptype.h"
#include "math.h"
#include "stdlib.h"
#include "bond_fene.h"
#include "atom.h"
#include "neighbor.h"
#include "domain.h"
#include "comm.h"
#include "update.h"
#include "force.h"
#include "memory.h"
#include "error.h"
using namespace LAMMPS_NS;
/* ---------------------------------------------------------------------- */
BondFENE::BondFENE(LAMMPS *lmp) : Bond(lmp)
{
TWO_1_3 = pow(2.0,(1.0/3.0));
}
/* ---------------------------------------------------------------------- */
BondFENE::~BondFENE()
{
if (allocated) {
memory->destroy(setflag);
memory->destroy(k);
memory->destroy(r0);
memory->destroy(epsilon);
memory->destroy(sigma);
}
}
/* ---------------------------------------------------------------------- */
void BondFENE::compute(int eflag, int vflag)
{
int i1,i2,n,type;
double delx,dely,delz,ebond,fbond;
double rsq,r0sq,rlogarg,sr2,sr6;
ebond = 0.0;
if (eflag || vflag) ev_setup(eflag,vflag);
else evflag = 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];
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);
// force from log term
rsq = delx*delx + dely*dely + delz*delz;
r0sq = r0[type] * r0[type];
rlogarg = 1.0 - rsq/r0sq;
// if r -> r0, then rlogarg < 0.0 which is an error
// issue a warning and reset rlogarg = epsilon
// if r > 2*r0 something serious is wrong, abort
if (rlogarg < 0.1) {
char str[128];
sprintf(str,"FENE bond too long: " BIGINT_FORMAT " %d %d %g",
update->ntimestep,atom->tag[i1],atom->tag[i2],sqrt(rsq));
error->warning(str,0);
if (rlogarg <= -3.0) error->one("Bad FENE bond");
rlogarg = 0.1;
}
fbond = -k[type]/rlogarg;
// force from LJ term
if (rsq < TWO_1_3*sigma[type]*sigma[type]) {
sr2 = sigma[type]*sigma[type]/rsq;
sr6 = sr2*sr2*sr2;
fbond += 48.0*epsilon[type]*sr6*(sr6-0.5)/rsq;
}
// energy
if (eflag) {
ebond = -0.5 * k[type]*r0sq*log(rlogarg);
if (rsq < TWO_1_3*sigma[type]*sigma[type])
ebond += 4.0*epsilon[type]*sr6*(sr6-1.0) + epsilon[type];
}
// apply force to each of 2 atoms
if (newton_bond || i1 < nlocal) {
f[i1][0] += delx*fbond;
f[i1][1] += dely*fbond;
f[i1][2] += delz*fbond;
}
if (newton_bond || i2 < nlocal) {
f[i2][0] -= delx*fbond;
f[i2][1] -= dely*fbond;
f[i2][2] -= delz*fbond;
}
if (evflag) ev_tally(i1,i2,nlocal,newton_bond,ebond,fbond,delx,dely,delz);
}
}
/* ---------------------------------------------------------------------- */
void BondFENE::allocate()
{
allocated = 1;
int n = atom->nbondtypes;
memory->create(k,n+1,"bond:k");
memory->create(r0,n+1,"bond:r0");
memory->create(epsilon,n+1,"bond:epsilon");
memory->create(sigma,n+1,"bond:sigma");
memory->create(setflag,n+1,"bond:setflag");
for (int i = 1; i <= n; i++) setflag[i] = 0;
}
/* ----------------------------------------------------------------------
set coeffs for one type
------------------------------------------------------------------------- */
void BondFENE::coeff(int narg, char **arg)
{
if (narg != 5) error->all("Incorrect args for bond coefficients");
if (!allocated) allocate();
int ilo,ihi;
force->bounds(arg[0],atom->nbondtypes,ilo,ihi);
double k_one = force->numeric(arg[1]);
double r0_one = force->numeric(arg[2]);
double epsilon_one = force->numeric(arg[3]);
double sigma_one = force->numeric(arg[4]);
int count = 0;
for (int i = ilo; i <= ihi; i++) {
k[i] = k_one;
r0[i] = r0_one;
epsilon[i] = epsilon_one;
sigma[i] = sigma_one;
setflag[i] = 1;
count++;
}
if (count == 0) error->all("Incorrect args for bond coefficients");
}
/* ----------------------------------------------------------------------
check if special_bond settings are valid
------------------------------------------------------------------------- */
void BondFENE::init_style()
{
// special bonds should be 0 1 1
if (force->special_lj[1] != 0.0 || force->special_lj[2] != 1.0 ||
force->special_lj[3] != 1.0) {
if (comm->me == 0)
error->warning("Use special bonds = 0,1,1 with bond style fene");
}
}
/* ---------------------------------------------------------------------- */
double BondFENE::equilibrium_distance(int i)
{
return 0.97*sigma[i];
}
/* ----------------------------------------------------------------------
proc 0 writes to restart file
------------------------------------------------------------------------- */
void BondFENE::write_restart(FILE *fp)
{
fwrite(&k[1],sizeof(double),atom->nbondtypes,fp);
fwrite(&r0[1],sizeof(double),atom->nbondtypes,fp);
fwrite(&epsilon[1],sizeof(double),atom->nbondtypes,fp);
fwrite(&sigma[1],sizeof(double),atom->nbondtypes,fp);
}
/* ----------------------------------------------------------------------
proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */
void BondFENE::read_restart(FILE *fp)
{
allocate();
if (comm->me == 0) {
fread(&k[1],sizeof(double),atom->nbondtypes,fp);
fread(&r0[1],sizeof(double),atom->nbondtypes,fp);
fread(&epsilon[1],sizeof(double),atom->nbondtypes,fp);
fread(&sigma[1],sizeof(double),atom->nbondtypes,fp);
}
MPI_Bcast(&k[1],atom->nbondtypes,MPI_DOUBLE,0,world);
MPI_Bcast(&r0[1],atom->nbondtypes,MPI_DOUBLE,0,world);
MPI_Bcast(&epsilon[1],atom->nbondtypes,MPI_DOUBLE,0,world);
MPI_Bcast(&sigma[1],atom->nbondtypes,MPI_DOUBLE,0,world);
for (int i = 1; i <= atom->nbondtypes; i++) setflag[i] = 1;
}
/* ---------------------------------------------------------------------- */
double BondFENE::single(int type, double rsq, int i, int j)
{
double r0sq = r0[type] * r0[type];
double rlogarg = 1.0 - rsq/r0sq;
// if r -> r0, then rlogarg < 0.0 which is an error
// issue a warning and reset rlogarg = epsilon
// if r > 2*r0 something serious is wrong, abort
if (rlogarg < 0.1) {
char str[128];
sprintf(str,"FENE bond too long: " BIGINT_FORMAT " %g",
update->ntimestep,sqrt(rsq));
error->warning(str,0);
if (rlogarg <= -3.0) error->one("Bad FENE bond");
rlogarg = 0.1;
}
double eng = -0.5 * k[type]*r0sq*log(rlogarg);
if (rsq < TWO_1_3*sigma[type]*sigma[type]) {
double sr2,sr6;
sr2 = sigma[type]*sigma[type]/rsq;
sr6 = sr2*sr2*sr2;
eng += 4.0*epsilon[type]*sr6*(sr6-1.0) + epsilon[type];
}
return eng;
}

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