144 lines
4.0 KiB
C++
144 lines
4.0 KiB
C++
/* ----------------------------------------------------------------------
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LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
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http://lammps.sandia.gov, Sandia National Laboratories
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Steve Plimpton, sjplimp@sandia.gov
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Copyright (2003) Sandia Corporation. Under the terms of Contract
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DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
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certain rights in this software. This software is distributed under
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the GNU General Public License.
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See the README file in the top-level LAMMPS directory.
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------------------------------------------------------------------------- */
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#include "stdlib.h"
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#include "string.h"
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#include "fix_momentum.h"
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#include "atom.h"
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#include "domain.h"
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#include "group.h"
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#include "error.h"
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using namespace LAMMPS_NS;
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using namespace FixConst;
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/* ----------------------------------------------------------------------
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Contributing author: Naveen Michaud-Agrawal (Johns Hopkins U)
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------------------------------------------------------------------------- */
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/* ---------------------------------------------------------------------- */
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FixMomentum::FixMomentum(LAMMPS *lmp, int narg, char **arg) :
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Fix(lmp, narg, arg)
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{
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if (narg < 4) error->all(FLERR,"Illegal fix momentum command");
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nevery = atoi(arg[3]);
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if (nevery <= 0) error->all(FLERR,"Illegal fix momentum command");
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linear = angular = 0;
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int iarg = 4;
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while (iarg < narg) {
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if (strcmp(arg[iarg],"linear") == 0) {
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if (iarg+4 > narg) error->all(FLERR,"Illegal fix momentum command");
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linear = 1;
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xflag = atoi(arg[iarg+1]);
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yflag = atoi(arg[iarg+2]);
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zflag = atoi(arg[iarg+3]);
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iarg += 4;
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} else if (strcmp(arg[iarg],"angular") == 0) {
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angular = 1;
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iarg += 1;
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} else error->all(FLERR,"Illegal fix momentum command");
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}
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if (linear == 0 && angular == 0)
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error->all(FLERR,"Illegal fix momentum command");
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if (linear)
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if (xflag < 0 || xflag > 1 || yflag < 0 || yflag > 1 ||
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zflag < 0 || zflag > 1) error->all(FLERR,"Illegal fix momentum command");
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// cannot have 0 atoms in group
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if (group->count(igroup) == 0)
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error->all(FLERR,"Fix momentum group has no atoms");
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}
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/* ---------------------------------------------------------------------- */
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int FixMomentum::setmask()
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{
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int mask = 0;
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mask |= END_OF_STEP;
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return mask;
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}
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/* ---------------------------------------------------------------------- */
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void FixMomentum::init()
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{
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masstotal = group->mass(igroup);
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}
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/* ---------------------------------------------------------------------- */
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void FixMomentum::end_of_step()
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{
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if (linear) {
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double vcm[3];
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group->vcm(igroup,masstotal,vcm);
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// adjust velocities by vcm to zero linear momentum
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// only adjust a component if flag is set
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double **v = atom->v;
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int *mask = atom->mask;
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int nlocal = atom->nlocal;
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for (int i = 0; i < nlocal; i++)
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if (mask[i] & groupbit) {
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if (xflag) v[i][0] -= vcm[0];
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if (yflag) v[i][1] -= vcm[1];
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if (zflag) v[i][2] -= vcm[2];
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}
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}
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if (angular) {
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double xcm[3],angmom[3],inertia[3][3],omega[3];
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group->xcm(igroup,masstotal,xcm);
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group->angmom(igroup,xcm,angmom);
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group->inertia(igroup,xcm,inertia);
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group->omega(angmom,inertia,omega);
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// adjust velocities to zero omega
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// vnew_i = v_i - w x r_i
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// must use unwrapped coords to compute r_i correctly
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double **x = atom->x;
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double **v = atom->v;
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int *mask = atom->mask;
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int *image = atom->image;
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int nlocal = atom->nlocal;
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int xbox,ybox,zbox;
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double dx,dy,dz;
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double xprd = domain->xprd;
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double yprd = domain->yprd;
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double zprd = domain->zprd;
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for (int i = 0; i < nlocal; i++)
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if (mask[i] & groupbit) {
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xbox = (image[i] & 1023) - 512;
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ybox = (image[i] >> 10 & 1023) - 512;
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zbox = (image[i] >> 20) - 512;
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dx = (x[i][0] + xbox*xprd) - xcm[0];
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dy = (x[i][1] + ybox*yprd) - xcm[1];
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dz = (x[i][2] + zbox*zprd) - xcm[2];
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v[i][0] -= omega[1]*dz - omega[2]*dy;
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v[i][1] -= omega[2]*dx - omega[0]*dz;
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v[i][2] -= omega[0]*dy - omega[1]*dx;
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}
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}
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}
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