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angle_cosine_periodic_omp.cpp
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Sat, May 25, 16:59

angle_cosine_periodic_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
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: Axel Kohlmeyer (Temple U)
------------------------------------------------------------------------- */
#include "angle_cosine_periodic_omp.h"
#include "atom.h"
#include "comm.h"
#include "force.h"
#include "neighbor.h"
#include "domain.h"
#include "math_const.h"
#include <math.h>
#include "suffix.h"
using namespace LAMMPS_NS;
using namespace MathConst;
#define SMALL 0.001
/* ---------------------------------------------------------------------- */
AngleCosinePeriodicOMP::AngleCosinePeriodicOMP(class LAMMPS *lmp)
: AngleCosinePeriodic(lmp), ThrOMP(lmp,THR_ANGLE)
{
suffix_flag |= Suffix::OMP;
}
/* ---------------------------------------------------------------------- */
void AngleCosinePeriodicOMP::compute(int eflag, int vflag)
{
if (eflag || vflag) {
ev_setup(eflag,vflag);
} else evflag = 0;
const int nall = atom->nlocal + atom->nghost;
const int nthreads = comm->nthreads;
const int inum = neighbor->nanglelist;
#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);
if (evflag) {
if (eflag) {
if (force->newton_bond) eval<1,1,1>(ifrom, ito, thr);
else eval<1,1,0>(ifrom, ito, thr);
} else {
if (force->newton_bond) eval<1,0,1>(ifrom, ito, thr);
else eval<1,0,0>(ifrom, ito, thr);
}
} else {
if (force->newton_bond) 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 EVFLAG, int EFLAG, int NEWTON_BOND>
void AngleCosinePeriodicOMP::eval(int nfrom, int nto, ThrData * const thr)
{
int i,i1,i2,i3,n,m,type,b_factor;
double delx1,dely1,delz1,delx2,dely2,delz2;
double eangle,f1[3],f3[3];
double rsq1,rsq2,r1,r2,c,s,a,a11,a12,a22;
double tn,tn_1,tn_2,un,un_1,un_2;
const double * const * const x = atom->x;
double * const * const f = thr->get_f();
const int * const * const anglelist = neighbor->anglelist;
const int nlocal = atom->nlocal;
for (n = nfrom; n < nto; n++) {
i1 = anglelist[n][0];
i2 = anglelist[n][1];
i3 = anglelist[n][2];
type = anglelist[n][3];
// 1st bond
delx1 = x[i1][0] - x[i2][0];
dely1 = x[i1][1] - x[i2][1];
delz1 = x[i1][2] - x[i2][2];
rsq1 = delx1*delx1 + dely1*dely1 + delz1*delz1;
r1 = sqrt(rsq1);
// 2nd bond
delx2 = x[i3][0] - x[i2][0];
dely2 = x[i3][1] - x[i2][1];
delz2 = x[i3][2] - x[i2][2];
rsq2 = delx2*delx2 + dely2*dely2 + delz2*delz2;
r2 = sqrt(rsq2);
// c = cosine of angle
c = delx1*delx2 + dely1*dely2 + delz1*delz2;
c /= r1*r2;
if (c > 1.0) c = 1.0;
if (c < -1.0) c = -1.0;
m = multiplicity[type];
b_factor = b[type];
// cos(n*x) = Tn(cos(x))
// Tn(x) = Chebyshev polynomials of the first kind: T_0 = 1, T_1 = x, ...
// recurrence relationship:
// Tn(x) = 2*x*T[n-1](x) - T[n-2](x) where T[-1](x) = 0
// also, dTn(x)/dx = n*U[n-1](x)
// where Un(x) = 2*x*U[n-1](x) - U[n-2](x) and U[-1](x) = 0
// finally need to handle special case for n = 1
tn = 1.0;
tn_1 = 1.0;
tn_2 = 0.0;
un = 1.0;
un_1 = 2.0;
un_2 = 0.0;
s = sqrt(1.0 - c*c);
if (s < SMALL) s = SMALL;
s = 1.0/s;
// force & energy
tn_2 = c;
for (i = 1; i <= m; i++) {
tn = 2*c*tn_1 - tn_2;
tn_2 = tn_1;
tn_1 = tn;
}
for (i = 2; i <= m; i++) {
un = 2*c*un_1 - un_2;
un_2 = un_1;
un_1 = un;
}
tn = b_factor*pow(-1.0,(double)m)*tn;
un = b_factor*pow(-1.0,(double)m)*m*un;
if (EFLAG) eangle = 2*k[type]*(1.0 - tn);
a = -k[type]*un;
a11 = a*c / rsq1;
a12 = -a / (r1*r2);
a22 = a*c / rsq2;
f1[0] = a11*delx1 + a12*delx2;
f1[1] = a11*dely1 + a12*dely2;
f1[2] = a11*delz1 + a12*delz2;
f3[0] = a22*delx2 + a12*delx1;
f3[1] = a22*dely2 + a12*dely1;
f3[2] = a22*delz2 + a12*delz1;
// apply force to each of 3 atoms
if (NEWTON_BOND || i1 < nlocal) {
f[i1][0] += f1[0];
f[i1][1] += f1[1];
f[i1][2] += f1[2];
}
if (NEWTON_BOND || i2 < nlocal) {
f[i2][0] -= f1[0] + f3[0];
f[i2][1] -= f1[1] + f3[1];
f[i2][2] -= f1[2] + f3[2];
}
if (NEWTON_BOND || i3 < nlocal) {
f[i3][0] += f3[0];
f[i3][1] += f3[1];
f[i3][2] += f3[2];
}
if (EVFLAG) ev_tally_thr(this,i1,i2,i3,nlocal,NEWTON_BOND,eangle,f1,f3,
delx1,dely1,delz1,delx2,dely2,delz2,thr);
}
}

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