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lammps/src/USER-OMP/pair_brownian_omp.cpp
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pair_brownian_omp.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
This software is distributed under the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
Contributing author: Axel Kohlmeyer (Temple U)
------------------------------------------------------------------------- */
#include "math.h"
#include "pair_brownian_omp.h"
#include "atom.h"
#include "comm.h"
#include "force.h"
#include "neighbor.h"
#include "neigh_list.h"
#include "update.h"
#include "random_mars.h"
#include "math_const.h"
using namespace LAMMPS_NS;
using namespace MathConst;
#define EPSILON 1.0e-10
/* ---------------------------------------------------------------------- */
PairBrownianOMP::PairBrownianOMP(LAMMPS *lmp) :
PairBrownian(lmp), ThrOMP(lmp, THR_PAIR)
{
respa_enable = 0;
random_thr = NULL;
}
/* ---------------------------------------------------------------------- */
PairBrownianOMP::~PairBrownianOMP()
{
if (random_thr) {
for (int i=1; i < comm->nthreads; ++i)
delete random_thr[i];
delete[] random_thr;
random_thr = NULL;
}
}
/* ---------------------------------------------------------------------- */
void PairBrownianOMP::compute(int eflag, int vflag)
{
if (eflag || vflag) {
ev_setup(eflag,vflag);
} else evflag = vflag_fdotr = 0;
const int nall = atom->nlocal + atom->nghost;
const int nthreads = comm->nthreads;
const int inum = list->inum;
if (!random_thr)
random_thr = new RanMars*[nthreads];
// to ensure full compatibility with the serial Brownian style
// we use is random number generator instance for thread 0
random_thr[0] = random;
#if defined(_OPENMP)
#pragma omp parallel default(none) shared(eflag,vflag)
#endif
{
int ifrom, ito, tid;
loop_setup_thr(ifrom, ito, tid, inum, nthreads);
ThrData *thr = fix->get_thr(tid);
ev_setup_thr(eflag, vflag, nall, eatom, vatom, thr);
// generate a random number generator instance for
// all threads != 0. make sure we use unique seeds.
if (random_thr && tid > 0)
random_thr[tid] = new RanMars(Pair::lmp, seed + comm->me
+ comm->nprocs*tid);
if (flaglog) {
if (evflag) {
if (force->newton_pair) eval<1,1,1>(ifrom, ito, thr);
else eval<1,1,0>(ifrom, ito, thr);
} else {
if (force->newton_pair) eval<1,0,1>(ifrom, ito, thr);
else eval<1,0,0>(ifrom, ito, thr);
}
} else {
if (evflag) {
if (force->newton_pair) eval<0,1,1>(ifrom, ito, thr);
else eval<0,1,0>(ifrom, ito, thr);
} else {
if (force->newton_pair) eval<0,0,1>(ifrom, ito, thr);
else eval<0,0,0>(ifrom, ito, thr);
}
}
reduce_thr(this, eflag, vflag, thr);
} // end of omp parallel region
}
template <int FLAGLOG, int EVFLAG, int NEWTON_PAIR>
void PairBrownianOMP::eval(int iifrom, int iito, ThrData * const thr)
{
int i,j,ii,jj,jnum,itype,jtype;
double xtmp,ytmp,ztmp,delx,dely,delz,fx,fy,fz,tx,ty,tz;
double rsq,r,h_sep,radi;
int *ilist,*jlist,*numneigh,**firstneigh;
const double * const * const x = atom->x;
double * const * const f = thr->get_f();
double * const * const torque = thr->get_torque();
const double * const radius = atom->radius;
const int * const type = atom->type;
const int nlocal = atom->nlocal;
RanMars &rng = *random_thr[thr->get_tid()];
double vxmu2f = force->vxmu2f;
double randr;
double prethermostat;
double xl[3],a_sq,a_sh,a_pu,Fbmag;
double p1[3],p2[3],p3[3];
int overlaps = 0;
// scale factor for Brownian moments
prethermostat = sqrt(24.0*force->boltz*t_target/update->dt);
prethermostat *= sqrt(force->vxmu2f/force->ftm2v/force->mvv2e);
ilist = list->ilist;
numneigh = list->numneigh;
firstneigh = list->firstneigh;
// loop over neighbors of my atoms
for (ii = iifrom; ii < iito; ++ii) {
i = ilist[ii];
xtmp = x[i][0];
ytmp = x[i][1];
ztmp = x[i][2];
itype = type[i];
radi = radius[i];
jlist = firstneigh[i];
jnum = numneigh[i];
// FLD contribution to force and torque due to isotropic terms
if (flagfld) {
f[i][0] += prethermostat*sqrt(R0)*(rng.uniform()-0.5);
f[i][1] += prethermostat*sqrt(R0)*(rng.uniform()-0.5);
f[i][2] += prethermostat*sqrt(R0)*(rng.uniform()-0.5);
if (FLAGLOG) {
torque[i][0] += prethermostat*sqrt(RT0)*(rng.uniform()-0.5);
torque[i][1] += prethermostat*sqrt(RT0)*(rng.uniform()-0.5);
torque[i][2] += prethermostat*sqrt(RT0)*(rng.uniform()-0.5);
}
}
for (jj = 0; jj < jnum; jj++) {
j = jlist[jj];
j &= NEIGHMASK;
delx = xtmp - x[j][0];
dely = ytmp - x[j][1];
delz = ztmp - x[j][2];
rsq = delx*delx + dely*dely + delz*delz;
jtype = type[j];
if (rsq < cutsq[itype][jtype]) {
r = sqrt(rsq);
// scalar resistances a_sq and a_sh
h_sep = r - 2.0*radi;
// check for overlaps
if (h_sep < 0.0) overlaps++;
// if less than minimum gap, use minimum gap instead
if (r < cut_inner[itype][jtype])
h_sep = cut_inner[itype][jtype] - 2.0*radi;
// scale h_sep by radi
h_sep = h_sep/radi;
// scalar resistances
if (FLAGLOG) {
a_sq = 6.0*MY_PI*mu*radi*(1.0/4.0/h_sep + 9.0/40.0*log(1.0/h_sep));
a_sh = 6.0*MY_PI*mu*radi*(1.0/6.0*log(1.0/h_sep));
a_pu = 8.0*MY_PI*mu*pow(radi,3)*(3.0/160.0*log(1.0/h_sep));
} else
a_sq = 6.0*MY_PI*mu*radi*(1.0/4.0/h_sep);
// generate the Pairwise Brownian Force: a_sq
Fbmag = prethermostat*sqrt(a_sq);
// generate a random number
randr = rng.uniform()-0.5;
// contribution due to Brownian motion
fx = Fbmag*randr*delx/r;
fy = Fbmag*randr*dely/r;
fz = Fbmag*randr*delz/r;
// add terms due to a_sh
if (FLAGLOG) {
// generate two orthogonal vectors to the line of centers
p1[0] = delx/r; p1[1] = dely/r; p1[2] = delz/r;
set_3_orthogonal_vectors(p1,p2,p3);
// magnitude
Fbmag = prethermostat*sqrt(a_sh);
// force in each of the two directions
randr = rng.uniform()-0.5;
fx += Fbmag*randr*p2[0];
fy += Fbmag*randr*p2[1];
fz += Fbmag*randr*p2[2];
randr = rng.uniform()-0.5;
fx += Fbmag*randr*p3[0];
fy += Fbmag*randr*p3[1];
fz += Fbmag*randr*p3[2];
}
// scale forces to appropriate units
fx = vxmu2f*fx;
fy = vxmu2f*fy;
fz = vxmu2f*fz;
// sum to total force
f[i][0] -= fx;
f[i][1] -= fy;
f[i][2] -= fz;
if (NEWTON_PAIR || j < nlocal) {
//randr = rng.uniform()-0.5;
//fx = Fbmag*randr*delx/r;
//fy = Fbmag*randr*dely/r;
//fz = Fbmag*randr*delz/r;
f[j][0] += fx;
f[j][1] += fy;
f[j][2] += fz;
}
// torque due to the Brownian Force
if (FLAGLOG) {
// location of the point of closest approach on I from its center
xl[0] = -delx/r*radi;
xl[1] = -dely/r*radi;
xl[2] = -delz/r*radi;
// torque = xl_cross_F
tx = xl[1]*fz - xl[2]*fy;
ty = xl[2]*fx - xl[0]*fz;
tz = xl[0]*fy - xl[1]*fx;
// torque is same on both particles
torque[i][0] -= tx;
torque[i][1] -= ty;
torque[i][2] -= tz;
if (NEWTON_PAIR || j < nlocal) {
torque[j][0] -= tx;
torque[j][1] -= ty;
torque[j][2] -= tz;
}
// torque due to a_pu
Fbmag = prethermostat*sqrt(a_pu);
// force in each direction
randr = rng.uniform()-0.5;
tx = Fbmag*randr*p2[0];
ty = Fbmag*randr*p2[1];
tz = Fbmag*randr*p2[2];
randr = rng.uniform()-0.5;
tx += Fbmag*randr*p3[0];
ty += Fbmag*randr*p3[1];
tz += Fbmag*randr*p3[2];
// torque has opposite sign on two particles
torque[i][0] -= tx;
torque[i][1] -= ty;
torque[i][2] -= tz;
if (NEWTON_PAIR || j < nlocal) {
torque[j][0] += tx;
torque[j][1] += ty;
torque[j][2] += tz;
}
}
if (EVFLAG) ev_tally_xyz(i,j,nlocal,NEWTON_PAIR,
0.0,0.0,-fx,-fy,-fz,delx,dely,delz);
}
}
}
}
/* ---------------------------------------------------------------------- */
double PairBrownianOMP::memory_usage()
{
double bytes = memory_usage_thr();
bytes += PairBrownian::memory_usage();
bytes += comm->nthreads * sizeof(RanMars*);
bytes += comm->nthreads * sizeof(RanMars);
return bytes;
}
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