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fix_rigid_nve.cpp
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Thu, Nov 7, 13:20

fix_rigid_nve.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: Tony Sheh (U Michigan), Trung Dac Nguyen (U Michigan)
references: Kamberaj et al., J. Chem. Phys. 122, 224114 (2005)
Miller et al., J Chem Phys. 116, 8649-8659
------------------------------------------------------------------------- */
#include "math.h"
#include "stdio.h"
#include "string.h"
#include "fix_rigid_nve.h"
#include "math_extra.h"
#include "atom.h"
#include "domain.h"
#include "update.h"
#include "modify.h"
#include "group.h"
#include "comm.h"
#include "force.h"
#include "output.h"
#include "memory.h"
#include "error.h"
using namespace LAMMPS_NS;
/* ---------------------------------------------------------------------- */
FixRigidNVE::FixRigidNVE(LAMMPS *lmp, int narg, char **arg) :
FixRigid(lmp, narg, arg)
{
memory->create(conjqm,nbody,4,"rigid/nve:conjqm");
}
/* ---------------------------------------------------------------------- */
FixRigidNVE::~FixRigidNVE()
{
memory->destroy(conjqm);
}
/* ---------------------------------------------------------------------- */
void FixRigidNVE::setup(int vflag)
{
FixRigid::setup(vflag);
double mbody[3];
for (int ibody = 0; ibody < nbody; ibody++) {
MathExtra::transpose_matvec(ex_space[ibody],ey_space[ibody],ez_space[ibody],
angmom[ibody],mbody);
MathExtra::quatvec(quat[ibody],mbody,conjqm[ibody]);
conjqm[ibody][0] *= 2.0;
conjqm[ibody][1] *= 2.0;
conjqm[ibody][2] *= 2.0;
conjqm[ibody][3] *= 2.0;
}
}
/* ----------------------------------------------------------------------
perform preforce velocity Verlet integration
see Kamberaj paper for step references
------------------------------------------------------------------------- */
void FixRigidNVE::initial_integrate(int vflag)
{
double dtfm,mbody[3],tbody[3],fquat[4];
double dtf2 = dtf * 2.0;
for (int ibody = 0; ibody < nbody; ibody++) {
// step 1.1 - update vcm by 1/2 step
dtfm = dtf / masstotal[ibody];
vcm[ibody][0] += dtfm * fcm[ibody][0] * fflag[ibody][0];
vcm[ibody][1] += dtfm * fcm[ibody][1] * fflag[ibody][1];
vcm[ibody][2] += dtfm * fcm[ibody][2] * fflag[ibody][2];
// step 1.2 - update xcm by full step
xcm[ibody][0] += dtv * vcm[ibody][0];
xcm[ibody][1] += dtv * vcm[ibody][1];
xcm[ibody][2] += dtv * vcm[ibody][2];
// step 1.3 - apply torque (body coords) to quaternion momentum
torque[ibody][0] *= tflag[ibody][0];
torque[ibody][1] *= tflag[ibody][1];
torque[ibody][2] *= tflag[ibody][2];
MathExtra::transpose_matvec(ex_space[ibody],ey_space[ibody],ez_space[ibody],
torque[ibody],tbody);
MathExtra::quatvec(quat[ibody],tbody,fquat);
conjqm[ibody][0] += dtf2 * fquat[0];
conjqm[ibody][1] += dtf2 * fquat[1];
conjqm[ibody][2] += dtf2 * fquat[2];
conjqm[ibody][3] += dtf2 * fquat[3];
// step 1.4 to 1.13 - use no_squish rotate to update p and q
no_squish_rotate(3,conjqm[ibody],quat[ibody],inertia[ibody],dtq);
no_squish_rotate(2,conjqm[ibody],quat[ibody],inertia[ibody],dtq);
no_squish_rotate(1,conjqm[ibody],quat[ibody],inertia[ibody],dtv);
no_squish_rotate(2,conjqm[ibody],quat[ibody],inertia[ibody],dtq);
no_squish_rotate(3,conjqm[ibody],quat[ibody],inertia[ibody],dtq);
// update exyz_space
// transform p back to angmom
// update angular velocity
MathExtra::q_to_exyz(quat[ibody],ex_space[ibody],ey_space[ibody],
ez_space[ibody]);
MathExtra::invquatvec(quat[ibody],conjqm[ibody],mbody);
MathExtra::matvec(ex_space[ibody],ey_space[ibody],ez_space[ibody],
mbody,angmom[ibody]);
angmom[ibody][0] *= 0.5;
angmom[ibody][1] *= 0.5;
angmom[ibody][2] *= 0.5;
MathExtra::angmom_to_omega(angmom[ibody],ex_space[ibody],ey_space[ibody],
ez_space[ibody],inertia[ibody],omega[ibody]);
}
// virial setup before call to set_xv
if (vflag) v_setup(vflag);
else evflag = 0;
// set coords/orient and velocity/rotation of atoms in rigid bodies
// from quarternion and omega
set_xv();
}
/* ---------------------------------------------------------------------- */
void FixRigidNVE::final_integrate()
{
int i,ibody;
double dtfm,xy,xz,yz;
// sum over atoms to get force and torque on rigid body
int *image = atom->image;
double **x = atom->x;
double **f = atom->f;
int nlocal = atom->nlocal;
double xprd = domain->xprd;
double yprd = domain->yprd;
double zprd = domain->zprd;
if (triclinic) {
xy = domain->xy;
xz = domain->xz;
yz = domain->yz;
}
int xbox,ybox,zbox;
double xunwrap,yunwrap,zunwrap,dx,dy,dz;
for (ibody = 0; ibody < nbody; ibody++)
for (i = 0; i < 6; i++) sum[ibody][i] = 0.0;
for (i = 0; i < nlocal; i++) {
if (body[i] < 0) continue;
ibody = body[i];
sum[ibody][0] += f[i][0];
sum[ibody][1] += f[i][1];
sum[ibody][2] += f[i][2];
xbox = (image[i] & 1023) - 512;
ybox = (image[i] >> 10 & 1023) - 512;
zbox = (image[i] >> 20) - 512;
if (triclinic == 0) {
xunwrap = x[i][0] + xbox*xprd;
yunwrap = x[i][1] + ybox*yprd;
zunwrap = x[i][2] + zbox*zprd;
} else {
xunwrap = x[i][0] + xbox*xprd + ybox*xy + zbox*xz;
yunwrap = x[i][1] + ybox*yprd + zbox*yz;
zunwrap = x[i][2] + zbox*zprd;
}
dx = xunwrap - xcm[ibody][0];
dy = yunwrap - xcm[ibody][1];
dz = zunwrap - xcm[ibody][2];
sum[ibody][3] += dy*f[i][2] - dz*f[i][1];
sum[ibody][4] += dz*f[i][0] - dx*f[i][2];
sum[ibody][5] += dx*f[i][1] - dy*f[i][0];
}
// extended particles add their torque to torque of body
if (extended) {
double **torque_one = atom->torque;
for (i = 0; i < nlocal; i++) {
if (body[i] < 0) continue;
ibody = body[i];
if (eflags[i] & TORQUE) {
sum[ibody][3] += torque_one[i][0];
sum[ibody][4] += torque_one[i][1];
sum[ibody][5] += torque_one[i][2];
}
}
}
MPI_Allreduce(sum[0],all[0],6*nbody,MPI_DOUBLE,MPI_SUM,world);
// update vcm and angmom
// include Langevin thermostat forces
// fflag,tflag = 0 for some dimensions in 2d
double mbody[3],tbody[3],fquat[4];
double dtf2 = dtf * 2.0;
for (ibody = 0; ibody < nbody; ibody++) {
fcm[ibody][0] = all[ibody][0] + langextra[ibody][0];
fcm[ibody][1] = all[ibody][1] + langextra[ibody][1];
fcm[ibody][2] = all[ibody][2] + langextra[ibody][2];
torque[ibody][0] = all[ibody][3] + langextra[ibody][3];
torque[ibody][1] = all[ibody][4] + langextra[ibody][4];
torque[ibody][2] = all[ibody][5] + langextra[ibody][5];
// update vcm by 1/2 step
dtfm = dtf / masstotal[ibody];
vcm[ibody][0] += dtfm * fcm[ibody][0] * fflag[ibody][0];
vcm[ibody][1] += dtfm * fcm[ibody][1] * fflag[ibody][1];
vcm[ibody][2] += dtfm * fcm[ibody][2] * fflag[ibody][2];
// update conjqm, then transform to angmom, set velocity again
// virial is already setup from initial_integrate
torque[ibody][0] *= tflag[ibody][0];
torque[ibody][1] *= tflag[ibody][1];
torque[ibody][2] *= tflag[ibody][2];
MathExtra::transpose_matvec(ex_space[ibody],ey_space[ibody],ez_space[ibody],
torque[ibody],tbody);
MathExtra::quatvec(quat[ibody],tbody,fquat);
conjqm[ibody][0] += dtf2 * fquat[0];
conjqm[ibody][1] += dtf2 * fquat[1];
conjqm[ibody][2] += dtf2 * fquat[2];
conjqm[ibody][3] += dtf2 * fquat[3];
MathExtra::invquatvec(quat[ibody],conjqm[ibody],mbody);
MathExtra::matvec(ex_space[ibody],ey_space[ibody],ez_space[ibody],
mbody,angmom[ibody]);
angmom[ibody][0] *= 0.5;
angmom[ibody][1] *= 0.5;
angmom[ibody][2] *= 0.5;
MathExtra::angmom_to_omega(angmom[ibody],ex_space[ibody],ey_space[ibody],
ez_space[ibody],inertia[ibody],omega[ibody]);
}
// set velocity/rotation of atoms in rigid bodies
// virial is already setup from initial_integrate
set_v();
}

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