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fix_wall_piston.cpp
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Sat, Nov 9, 18:02

fix_wall_piston.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 "math.h"
#include "string.h"
#include "stdlib.h"
#include "fix_wall_piston.h"
#include "atom.h"
#include "modify.h"
#include "domain.h"
#include "lattice.h"
#include "update.h"
#include "error.h"
#include "random_mars.h"
#include "force.h"
#include "comm.h"
using namespace LAMMPS_NS;
/* ---------------------------------------------------------------------- */
FixWallPiston::FixWallPiston(LAMMPS *lmp, int narg, char **arg) :
Fix(lmp, narg, arg)
{
force_reneighbor = 1;
next_reneighbor = -1;
box_change = 1;
time_depend = 1;
if (narg < 4) error->all("Illegal fix wall/piston command");
randomt = NULL;
tempflag = 0;
scaleflag = 1;
roughflag = 0;
rampflag = 0;
rampNL1flag = 0;
rampNL2flag = 0;
rampNL3flag = 0;
rampNL4flag = 0;
rampNL5flag = 0;
x0 = y0 = z0 = vx = vy = vz = 0.0;
xloflag = xhiflag = yloflag = yhiflag = zloflag = zhiflag = 0;
int iarg = 0;
iarg = 3;
while (iarg < narg) {
if (strcmp(arg[iarg],"xlo") == 0) { error->all("Fix wall/piston command only available at zlo");
} else if (strcmp(arg[iarg],"ylo") == 0) { error->all("Fix wall/piston command only available at zlo");
} else if (strcmp(arg[iarg],"zlo") == 0) {
zloflag = 1;
iarg++;
if (domain->boundary[2][0] != 2) error->all("Must shrink-wrap piston boundary");
} else if (strcmp(arg[iarg],"xhi") == 0) { error->all("Fix wall/piston command only available at zlo");
} else if (strcmp(arg[iarg],"yhi") == 0) { error->all("Fix wall/piston command only available at zlo");
} else if (strcmp(arg[iarg],"zhi") == 0) { error->all("Fix wall/piston command only available at zlo");
} else if (strcmp(arg[iarg],"vel") == 0) {
if (iarg+4 > narg) error->all("Illegal fix wall/piston command");
vx = atof(arg[iarg+1]);
vy = atof(arg[iarg+2]);
vz = atof(arg[iarg+3]);
iarg += 4;
} else if (strcmp(arg[iarg],"pos") == 0) {
if (iarg+4 > narg) error->all("Illegal fix wall/piston command");
x0 = atof(arg[iarg+1]);
y0 = atof(arg[iarg+2]);
z0 = atof(arg[iarg+3]);
iarg += 4;
} else if (strcmp(arg[iarg],"temp") == 0) {
if (iarg+5 > narg) error->all("Illegal fix wall/pistons command");
tempflag = 1;
t_target = atof(arg[iarg+1]);
t_period = atof(arg[iarg+2]);
tseed = atoi(arg[iarg+3]);
t_extent = atof(arg[iarg+4]);
if (t_target <= 0) error->all("Illegal fix wall/piston command");
if (t_period <= 0) error->all("Illegal fix wall/piston command");
if (t_extent <= 0) error->all("Illegal fix wall/piston command");
if (tseed <= 0) error->all("Illegal fix wall/pistons command");
randomt = new RanMars(lmp,tseed + comm->me);
gfactor1 = new double[atom->ntypes+1];
gfactor2 = new double[atom->ntypes+1];
iarg += 5;
} else if (strcmp(arg[iarg],"rough") == 0) {
roughflag = 1;
roughdist = atof(arg[iarg+1]);
iarg += 2;
} else if (strcmp(arg[iarg],"ramp") == 0) {
rampflag = 1;
iarg++;
} else if (strcmp(arg[iarg],"rampNL1") == 0) {
rampNL1flag = 1;
iarg++;
} else if (strcmp(arg[iarg],"rampNL2") == 0) {
rampNL2flag = 1;
iarg++;
} else if (strcmp(arg[iarg],"rampNL3") == 0) {
rampNL3flag = 1;
iarg++;
} else if (strcmp(arg[iarg],"rampNL4") == 0) {
rampNL4flag = 1;
iarg++;
} else if (strcmp(arg[iarg],"rampNL5") == 0) {
rampNL5flag = 1;
iarg++;
} else if (strcmp(arg[iarg],"units") == 0) {
if (iarg+2 > narg) error->all("Illegal fix wall/piston command");
if (strcmp(arg[iarg+1],"box") == 0) scaleflag = 0;
else if (strcmp(arg[iarg+1],"lattice") == 0) scaleflag = 1;
else error->all("Illegal fix wall/piston command");
iarg += 2;
} else error->all("Illegal fix wall/piston command");
}
if (vx < 0.0 || vy < 0.0 || vz < 0.0) error->all("Illegal fix wall/piston velocity");
if ((xloflag || xhiflag) && domain->xperiodic)
error->all("Cannot use wall in periodic dimension");
if ((yloflag || yhiflag) && domain->yperiodic)
error->all("Cannot use wall in periodic dimension");
if ((zloflag || zhiflag) && domain->zperiodic)
error->all("Cannot use wall in periodic dimension");
// setup scaling
if (scaleflag && domain->lattice == NULL)
error->all("Use of fix wall/piston with undefined lattice");
double xscale,yscale,zscale;
if (scaleflag) {
xscale = domain->lattice->xlattice;
yscale = domain->lattice->ylattice;
zscale = domain->lattice->zlattice;
}
else xscale = yscale = zscale = 1.0;
vx *= xscale;
vy *= yscale;
vz *= zscale;
x0 *= xscale;
y0 *= yscale;
z0 *= zscale;
roughdist *= zscale;
if (rampflag || rampNL1flag || rampNL2flag || rampNL3flag || rampNL4flag || rampNL5flag) {
maxvx = vx;
maxvy = vy;
maxvz = vz;
}
}
/* ---------------------------------------------------------------------- */
int FixWallPiston::setmask()
{
int mask = 0;
mask |= POST_INTEGRATE;
mask |= POST_INTEGRATE_RESPA;
mask |= INITIAL_INTEGRATE;
return mask;
}
/* ---------------------------------------------------------------------- */
void FixWallPiston::initial_integrate(int vflag)
{
next_reneighbor = update->ntimestep;
}
/* ---------------------------------------------------------------------- */
void FixWallPiston::post_integrate()
{
double xlo, xhi, ylo, yhi, zlo, zhi;
double **x = atom->x;
double **v = atom->v;
int *mask = atom->mask;
int nlocal = atom->nlocal;
double t = (update->ntimestep - update->beginstep) * update->dt;
double tott = (update->endstep - update->beginstep) * update->dt;
double tt = t * t;
double ttt = tt * t;
double tttt = tt * tt;
double t0p5 = sqrt(t/tott);
double t1p5 = t0p5*t0p5*t0p5;
double t2p5 = t1p5*t0p5*t0p5;
if (rampflag) {
paccelx = maxvx / tott;
paccely = maxvy / tott;
paccelz = maxvz / tott;
if (zloflag) { zlo = z0 + 0.5 * paccelz * tt; vz = paccelz * t; }
}
else if (rampNL1flag) {
paccelz = maxvz / tott;
angfreq = 6.283185 / (0.5 * tott);
if (zloflag) {
zlo = z0 + paccelz * (0.5*tt + 1.0/(angfreq*angfreq) - 1.0/(angfreq*angfreq)*cos(angfreq*t));
vz = paccelz * (t + 1.0/angfreq*sin(angfreq*t));
}
else { error->all("NL ramp in wall/piston only implemented in zlo for now"); }
}
else if (rampNL2flag) {
paccelz = maxvz / tott;
angfreq = 18.84956 / tott;
if (zloflag) {
zlo = z0 + paccelz * (0.5*tt + 4.0/(3.0*angfreq*angfreq)*(1.0-cos(angfreq*t)) + 1.0/(6.0*angfreq*angfreq)*(1.0-cos(2.0*angfreq*t)));
vz = paccelz * (t + 4.0/(3.0*angfreq)*sin(angfreq*t) + 1.0/(3.0*angfreq)*sin(2.0*angfreq*t));
}
else { error->all("NL ramp in wall/piston only implemented in zlo for now"); }
}
else if (rampNL3flag) {
paccelz = maxvz / tott;
if (zloflag) {
zlo = z0 + paccelz*tott*tott/2.5 * (t2p5 );
vz = paccelz * tott * (t1p5 );
}
else { error->all("NL ramp in wall/piston only implemented in zlo for now"); }
}
else if (rampNL4flag) {
paccelz = maxvz / tott;
if (zloflag) {
zlo = z0 + paccelz/tott/3.0 * (ttt);
vz = paccelz / tott * (tt);
}
else { error->all("NL ramp in wall/piston only implemented in zlo for now"); }
}
else if (rampNL5flag) {
paccelz = maxvz / tott;
if (zloflag) {
zlo = z0 + paccelz/tott/tott/4.0 * (tttt);
vz = paccelz / tott / tott * (ttt);
}
else { error->all("NL ramp in wall/piston only implemented in zlo for now"); }
}
else {
if (zloflag) { zlo = z0 + vz * t; }
}
if (update->ntimestep % 1000 == 0)
if (comm->me == 0) {
if (screen)
fprintf(screen,"SHOCK: step " BIGINT_FORMAT
" t %g zpos %g vz %g az %g zlo %g\n",
update->ntimestep, t, zlo, vz, paccelz, domain->boxlo[2]);
if (logfile)
fprintf(logfile,"SHOCK: step " BIGINT_FORMAT
" t %g zpos %g vz %g az %g zlo %g\n",
update->ntimestep, t, zlo, vz, paccelz, domain->boxlo[2]);
}
// VIRIAL PRESSURE CONTRIBUTION?
for (int i = 0; i < nlocal; i++) {
if (mask[i] & groupbit) {
roughoff = 0.0;
if (roughflag) {
roughoff += roughdist*fabs((x[i][0] - domain->boxlo[0])/(domain->boxhi[0]-domain->boxlo[0])-0.5);
roughoff += roughdist*fabs((x[i][1] - domain->boxlo[1])/(domain->boxhi[1]-domain->boxlo[1])-0.5);
}
if (zloflag && x[i][2] < zlo - roughoff) {
x[i][2] = 2.0 * (zlo - roughoff) - x[i][2];
v[i][2] = 2.0 * vz - v[i][2];
}
}
}
double **f = atom->f;
int *type = atom->type;
double gamma1,gamma2;
double tsqrt = sqrt(t_target);
if (atom->mass) {
if (tempflag) {
for (int i = 1; i <= atom->ntypes; i++) {
gfactor1[i] = -atom->mass[i] / t_period / force->ftm2v;
gfactor2[i] = sqrt(atom->mass[i]) *
sqrt(24.0*force->boltz/t_period/update->dt/force->mvv2e) /
force->ftm2v;
}
}
for (int i = 0; i < nlocal; i++) {
// SET TEMP AHEAD OF PISTON
if (tempflag && x[i][2] <= domain->boxlo[2] + t_extent ) {
gamma1 = gfactor1[type[i]];
gamma2 = gfactor2[type[i]] * tsqrt;
f[i][0] += gamma1*v[i][0] + gamma2*(randomt->uniform()-0.5);
f[i][1] += gamma1*v[i][1] + gamma2*(randomt->uniform()-0.5);
f[i][2] += gamma1*(v[i][2]-vz) + gamma2*(randomt->uniform()-0.5);
}
}
} else {
double *rmass = atom->rmass;
double boltz = force->boltz;
double dt = update->dt;
double mvv2e = force->mvv2e;
double ftm2v = force->ftm2v;
for (int i = 0; i < nlocal; i++) {
// SET TEMP AHEAD OF PISTON
if (tempflag && x[i][2] <= domain->boxlo[2] + t_extent ) {
gamma1 = -rmass[i] / t_period / ftm2v;
gamma2 = sqrt(rmass[i]) * sqrt(24.0*boltz/t_period/dt/mvv2e) / ftm2v;
gamma2 *= tsqrt;
f[i][0] += gamma1*v[i][0] + gamma2*(randomt->uniform()-0.5);
f[i][1] += gamma1*v[i][1] + gamma2*(randomt->uniform()-0.5);
f[i][2] += gamma1*v[i][2] + gamma2*(randomt->uniform()-0.5);
}
}
}
}

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