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fix_addtorque.cpp
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Tue, Jul 2, 18:25

fix_addtorque.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: Laurent Joly (U Lyon, France), ljoly.ulyon@gmail.com
------------------------------------------------------------------------- */
#include <string.h>
#include <stdlib.h>
#include "fix_addtorque.h"
#include "atom.h"
#include "update.h"
#include "modify.h"
#include "domain.h"
#include "respa.h"
#include "input.h"
#include "variable.h"
#include "memory.h"
#include "error.h"
#include "group.h"
#include "force.h"
using namespace LAMMPS_NS;
using namespace FixConst;
enum{NONE,CONSTANT,EQUAL,ATOM};
/* ---------------------------------------------------------------------- */
FixAddTorque::FixAddTorque(LAMMPS *lmp, int narg, char **arg) :
Fix(lmp, narg, arg)
{
if (narg != 6) error->all(FLERR,"Illegal fix addtorque command");
scalar_flag = 1;
vector_flag = 1;
size_vector = 3;
global_freq = 1;
extscalar = 1;
extvector = 1;
xstr = ystr = zstr = NULL;
if (strstr(arg[3],"v_") == arg[3]) {
int n = strlen(&arg[3][2]) + 1;
xstr = new char[n];
strcpy(xstr,&arg[3][2]);
} else {
xvalue = force->numeric(FLERR,arg[3]);
xstyle = CONSTANT;
}
if (strstr(arg[4],"v_") == arg[4]) {
int n = strlen(&arg[4][2]) + 1;
ystr = new char[n];
strcpy(ystr,&arg[4][2]);
} else {
yvalue = force->numeric(FLERR,arg[4]);
ystyle = CONSTANT;
}
if (strstr(arg[5],"v_") == arg[5]) {
int n = strlen(&arg[5][2]) + 1;
zstr = new char[n];
strcpy(zstr,&arg[5][2]);
} else {
zvalue = force->numeric(FLERR,arg[5]);
zstyle = CONSTANT;
}
force_flag = 0;
foriginal[0] = foriginal[1] = foriginal[2] = foriginal[3] = 0.0;
}
/* ---------------------------------------------------------------------- */
FixAddTorque::~FixAddTorque()
{
delete [] xstr;
delete [] ystr;
delete [] zstr;
}
/* ---------------------------------------------------------------------- */
int FixAddTorque::setmask()
{
int mask = 0;
mask |= POST_FORCE;
mask |= THERMO_ENERGY;
mask |= POST_FORCE_RESPA;
mask |= MIN_POST_FORCE;
return mask;
}
/* ---------------------------------------------------------------------- */
void FixAddTorque::init()
{
// check variables
if (xstr) {
xvar = input->variable->find(xstr);
if (xvar < 0)
error->all(FLERR,"Variable name for fix addtorque does not exist");
if (input->variable->equalstyle(xvar)) xstyle = EQUAL;
else error->all(FLERR,"Variable for fix addtorque is invalid style");
}
if (ystr) {
yvar = input->variable->find(ystr);
if (yvar < 0)
error->all(FLERR,"Variable name for fix addtorque does not exist");
if (input->variable->equalstyle(yvar)) ystyle = EQUAL;
else error->all(FLERR,"Variable for fix addtorque is invalid style");
}
if (zstr) {
zvar = input->variable->find(zstr);
if (zvar < 0)
error->all(FLERR,"Variable name for fix addtorque does not exist");
if (input->variable->equalstyle(zvar)) zstyle = EQUAL;
else error->all(FLERR,"Variable for fix addtorque is invalid style");
}
if (xstyle == EQUAL || ystyle == EQUAL || zstyle == EQUAL)
varflag = EQUAL;
else varflag = CONSTANT;
if (strcmp(update->integrate_style,"respa") == 0)
nlevels_respa = ((Respa *) update->integrate)->nlevels;
}
/* ---------------------------------------------------------------------- */
void FixAddTorque::setup(int vflag)
{
if (strcmp(update->integrate_style,"verlet") == 0)
post_force(vflag);
else {
((Respa *) update->integrate)->copy_flevel_f(nlevels_respa-1);
post_force_respa(vflag,nlevels_respa-1,0);
((Respa *) update->integrate)->copy_f_flevel(nlevels_respa-1);
}
}
/* ---------------------------------------------------------------------- */
void FixAddTorque::min_setup(int vflag)
{
post_force(vflag);
}
/* ---------------------------------------------------------------------- */
void FixAddTorque::post_force(int vflag)
{
double **x = atom->x;
double **f = atom->f;
int *mask = atom->mask;
int *type = atom->type;
imageint *image = atom->image;
double *mass = atom->mass;
double *rmass = atom->rmass;
int nlocal = atom->nlocal;
double mvv2e = force->mvv2e;
double dx,dy,dz,vx,vy,vz,fx,fy,fz,massone,omegadotr;
double tcm[3],xcm[3],angmom[3],omega[3],itorque[3],domegadt[3],tlocal[3];
double inertia[3][3];
double unwrap[3];
// foriginal[0] = "potential energy" for added force
// foriginal[123] = torque on atoms before extra force added
foriginal[0] = foriginal[1] = foriginal[2] = foriginal[3] = 0.0;
force_flag = 0;
if (varflag == EQUAL) {
// variable torque, wrap with clear/add
modify->clearstep_compute();
if (xstyle == EQUAL) xvalue = input->variable->compute_equal(xvar);
if (ystyle == EQUAL) yvalue = input->variable->compute_equal(yvar);
if (zstyle == EQUAL) zvalue = input->variable->compute_equal(zvar);
modify->addstep_compute(update->ntimestep + 1);
}
atom->check_mass();
double masstotal = group->mass(igroup);
group->xcm(igroup,masstotal,xcm);
group->inertia(igroup,xcm,inertia);
group->angmom(igroup,xcm,angmom);
group->omega(angmom,inertia,omega);
tlocal[0] = tlocal[1] = tlocal[2] = 0.0;
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
domain->unmap(x[i],image[i],unwrap);
dx = unwrap[0] - xcm[0];
dy = unwrap[1] - xcm[1];
dz = unwrap[2] - xcm[2];
if (rmass) massone = rmass[i];
else massone = mass[type[i]];
omegadotr = omega[0]*dx+omega[1]*dy+omega[2]*dz;
tlocal[0] += massone * omegadotr * (dy*omega[2] - dz*omega[1]);
tlocal[1] += massone * omegadotr * (dz*omega[0] - dx*omega[2]);
tlocal[2] += massone * omegadotr * (dx*omega[1] - dy*omega[0]);
}
MPI_Allreduce(tlocal,itorque,3,MPI_DOUBLE,MPI_SUM,world);
tcm[0] = xvalue - mvv2e*itorque[0];
tcm[1] = yvalue - mvv2e*itorque[1];
tcm[2] = zvalue - mvv2e*itorque[2];
group->omega(tcm,inertia,domegadt);
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
domain->unmap(x[i],image[i],unwrap);
dx = unwrap[0] - xcm[0];
dy = unwrap[1] - xcm[1];
dz = unwrap[2] - xcm[2];
vx = mvv2e*(dz*omega[1]-dy*omega[2]);
vy = mvv2e*(dx*omega[2]-dz*omega[0]);
vz = mvv2e*(dy*omega[0]-dx*omega[1]);
if (rmass) massone = rmass[i];
else massone = mass[type[i]];
fx = massone * (dz*domegadt[1]-dy*domegadt[2] + vz*omega[1]-vy*omega[2]);
fy = massone * (dx*domegadt[2]-dz*domegadt[0] + vx*omega[2]-vz*omega[0]);
fz = massone * (dy*domegadt[0]-dx*domegadt[1] + vy*omega[0]-vx*omega[1]);
// potential energy = - x dot f
foriginal[0] -= fx*x[i][0] + fy*x[i][1] + fz*x[i][2];
foriginal[1] += dy*f[i][2] - dz*f[i][1];
foriginal[2] += dz*f[i][0] - dx*f[i][2];
foriginal[3] += dx*f[i][1] - dy*f[i][0];
f[i][0] += fx;
f[i][1] += fy;
f[i][2] += fz;
}
}
/* ---------------------------------------------------------------------- */
void FixAddTorque::post_force_respa(int vflag, int ilevel, int iloop)
{
if (ilevel == nlevels_respa-1) post_force(vflag);
}
/* ---------------------------------------------------------------------- */
void FixAddTorque::min_post_force(int vflag)
{
post_force(vflag);
}
/* ----------------------------------------------------------------------
potential energy of added torque
------------------------------------------------------------------------- */
double FixAddTorque::compute_scalar()
{
// only sum across procs one time
if (force_flag == 0) {
MPI_Allreduce(foriginal,foriginal_all,4,MPI_DOUBLE,MPI_SUM,world);
force_flag = 1;
}
return foriginal_all[0];
}
/* ----------------------------------------------------------------------
return components of total torque on fix group before torque was changed
------------------------------------------------------------------------- */
double FixAddTorque::compute_vector(int n)
{
// only sum across procs one time
if (force_flag == 0) {
MPI_Allreduce(foriginal,foriginal_all,4,MPI_DOUBLE,MPI_SUM,world);
force_flag = 1;
}
return foriginal_all[n+1];
}

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