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pair_lj_charmm_coul_long_opt.cpp
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Wed, Feb 19, 00:11

pair_lj_charmm_coul_long_opt.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 authors:
James Fischer, High Performance Technologies, Inc.
David Richie, Stone Ridge Technology
Vincent Natoli, Stone Ridge Technology
------------------------------------------------------------------------- */
#include "math.h"
#include "stdlib.h"
#include "pair_lj_charmm_coul_long_opt.h"
#include "atom.h"
#include "force.h"
#include "neigh_list.h"
using namespace LAMMPS_NS;
#define EWALD_F 1.12837917
#define EWALD_P 0.3275911
#define EWALD_A1 0.254829592
#define EWALD_A2 -0.284496736
#define EWALD_A3 1.421413741
#define EWALD_A4 -1.453152027
#define EWALD_A5 1.061405429
/* ---------------------------------------------------------------------- */
PairLJCharmmCoulLongOpt::PairLJCharmmCoulLongOpt(LAMMPS *lmp) :
PairLJCharmmCoulLong(lmp) {}
/* ---------------------------------------------------------------------- */
void PairLJCharmmCoulLongOpt::compute(int eflag, int vflag)
{
if (eflag || vflag) ev_setup(eflag,vflag);
else evflag = vflag_fdotr = 0;
if (evflag) {
if (eflag) {
if (force->newton_pair) return eval<1,1,1>();
else return eval<1,1,0>();
} else {
if (force->newton_pair) return eval<1,0,1>();
else return eval<1,0,0>();
}
} else {
if (force->newton_pair) return eval<0,0,1>();
else return eval<0,0,0>();
}
}
/* ---------------------------------------------------------------------- */
template < int EVFLAG, int EFLAG, int NEWTON_PAIR >
void PairLJCharmmCoulLongOpt::eval()
{
typedef struct { double x,y,z; } vec3_t;
typedef struct {
double cutsq,lj1,lj2,lj3,lj4,offset;
double _pad[2];
} fast_alpha_t;
int i,j,ii,jj,inum,jnum,itype,jtype,itable,sbindex;
double fraction,table;
double r,r2inv,r6inv,forcecoul,forcelj,factor_coul,factor_lj;
double grij,expm2,prefactor,t,erfc;
double philj,switch1,switch2;
double rsq;
double evdwl = 0.0;
double ecoul = 0.0;
double** _noalias x = atom->x;
double** _noalias f = atom->f;
double* _noalias q = atom->q;
int* _noalias type = atom->type;
int nlocal = atom->nlocal;
double* _noalias special_coul = force->special_coul;
double* _noalias special_lj = force->special_lj;
double qqrd2e = force->qqrd2e;
inum = list->inum;
int* _noalias ilist = list->ilist;
int** _noalias firstneigh = list->firstneigh;
int* _noalias numneigh = list->numneigh;
vec3_t* _noalias xx = (vec3_t*)x[0];
vec3_t* _noalias ff = (vec3_t*)f[0];
int ntypes = atom->ntypes;
int ntypes2 = ntypes*ntypes;
double tmp_coef1 = 1.0/denom_lj;
double tmp_coef2 = cut_ljsq - 3.0*cut_lj_innersq;
fast_alpha_t* _noalias fast_alpha =
(fast_alpha_t*)malloc(ntypes2*sizeof(fast_alpha_t));
for (i = 0; i < ntypes; i++) for (j = 0; j < ntypes; j++) {
fast_alpha_t& a = fast_alpha[i*ntypes+j];
a.cutsq = cutsq[i+1][j+1];
a.lj1 = lj1[i+1][j+1];
a.lj2 = lj2[i+1][j+1];
a.lj3 = lj3[i+1][j+1];
a.lj4 = lj4[i+1][j+1];
}
fast_alpha_t* _noalias tabsix = fast_alpha;
// loop over neighbors of my atoms
for (ii = 0; ii < inum; ii++) {
i = ilist[ii];
double qtmp = q[i];
double xtmp = xx[i].x;
double ytmp = xx[i].y;
double ztmp = xx[i].z;
itype = type[i] - 1;
int* _noalias jlist = firstneigh[i];
jnum = numneigh[i];
double tmpfx = 0.0;
double tmpfy = 0.0;
double tmpfz = 0.0;
fast_alpha_t* _noalias tabsixi = (fast_alpha_t*) &tabsix[itype*ntypes];
for (jj = 0; jj < jnum; jj++) {
j = jlist[jj];
sbindex = sbmask(j);
if (sbindex == 0) {
double delx = xtmp - xx[j].x;
double dely = ytmp - xx[j].y;
double delz = ztmp - xx[j].z;
rsq = delx*delx + dely*dely + delz*delz;
double tmp_coef3 = qtmp*q[j];
if (rsq < cut_bothsq) {
r2inv = 1.0/rsq;
forcecoul = 0.0;
if (rsq < cut_coulsq) {
if (!ncoultablebits || rsq <= tabinnersq) {
r = sqrt(rsq);
grij = g_ewald * r;
expm2 = exp(-grij*grij);
t = 1.0 / (1.0 + EWALD_P*grij);
erfc = t *
(EWALD_A1+t*(EWALD_A2+t*(EWALD_A3+t*(EWALD_A4+t*EWALD_A5)))) *
expm2;
prefactor = qqrd2e * tmp_coef3/r;
forcecoul = prefactor * (erfc + EWALD_F*grij*expm2);
} else {
union_int_float_t rsq_lookup;
rsq_lookup.f = rsq;
itable = rsq_lookup.i & ncoulmask;
itable >>= ncoulshiftbits;
fraction = (rsq_lookup.f - rtable[itable]) * drtable[itable];
table = ftable[itable] + fraction*dftable[itable];
forcecoul = tmp_coef3 * table;
}
}
forcelj = 0.0;
if (rsq < cut_ljsq) {
r6inv = r2inv*r2inv*r2inv;
jtype = type[j] - 1;
fast_alpha_t& a = tabsixi[jtype];
forcelj = r6inv * (a.lj1*r6inv - a.lj2);
if (rsq > cut_lj_innersq) {
switch1 = (cut_ljsq-rsq) * (cut_ljsq-rsq) *
(tmp_coef2 + 2.0*rsq) * tmp_coef1;
switch2 = 12.0*rsq * (cut_ljsq-rsq) *
(rsq-cut_lj_innersq) * tmp_coef1;
philj = r6inv * (a.lj3*r6inv - a.lj4);
forcelj = forcelj*switch1 + philj*switch2;
}
}
double fpair = (forcecoul + forcelj) * r2inv;
tmpfx += delx*fpair;
tmpfy += dely*fpair;
tmpfz += delz*fpair;
if (NEWTON_PAIR || j < nlocal) {
ff[j].x -= delx*fpair;
ff[j].y -= dely*fpair;
ff[j].z -= delz*fpair;
}
if (EFLAG) {
if (rsq < cut_coulsq) {
if (!ncoultablebits || rsq <= tabinnersq)
ecoul = prefactor*erfc;
else {
table = etable[itable] + fraction*detable[itable];
ecoul = tmp_coef3 * table;
}
} else ecoul = 0.0;
if (rsq < cut_ljsq) {
fast_alpha_t& a = tabsixi[jtype];
evdwl = r6inv*(a.lj3*r6inv-a.lj4);
if (rsq > cut_lj_innersq) {
switch1 = (cut_ljsq-rsq) * (cut_ljsq-rsq) *
(tmp_coef2 + 2.0*rsq) * tmp_coef1;
evdwl *= switch1;
}
} else evdwl = 0.0;
}
if (EVFLAG) ev_tally(i,j,nlocal,NEWTON_PAIR,
evdwl,ecoul,fpair,delx,dely,delz);
}
} else {
factor_lj = special_lj[sbindex];
factor_coul = special_coul[sbindex];
j &= NEIGHMASK;
double delx = xtmp - xx[j].x;
double dely = ytmp - xx[j].y;
double delz = ztmp - xx[j].z;
rsq = delx*delx + dely*dely + delz*delz;
double tmp_coef3 = qtmp*q[j];
if (rsq < cut_bothsq) {
r2inv = 1.0/rsq;
forcecoul = 0.0;
if (rsq < cut_coulsq) {
if (!ncoultablebits || rsq <= tabinnersq) {
r = sqrt(rsq);
grij = g_ewald * r;
expm2 = exp(-grij*grij);
t = 1.0 / (1.0 + EWALD_P*grij);
erfc = t *
(EWALD_A1+t*(EWALD_A2+t*(EWALD_A3+t*(EWALD_A4+t*EWALD_A5)))) *
expm2;
prefactor = qqrd2e * tmp_coef3/r;
forcecoul = prefactor * (erfc + EWALD_F*grij*expm2);
if (factor_coul < 1.0) {
forcecoul -= (1.0-factor_coul)*prefactor;
}
} else {
union_int_float_t rsq_lookup;
rsq_lookup.f = rsq;
itable = rsq_lookup.i & ncoulmask;
itable >>= ncoulshiftbits;
fraction = (rsq_lookup.f - rtable[itable]) * drtable[itable];
table = ftable[itable] + fraction*dftable[itable];
forcecoul = tmp_coef3 * table;
if (factor_coul < 1.0) {
table = ctable[itable] + fraction*dctable[itable];
prefactor = tmp_coef3 * table;
forcecoul -= (1.0-factor_coul)*prefactor;
}
}
}
forcelj = 0.0;
if (rsq < cut_ljsq) {
r6inv = r2inv*r2inv*r2inv;
jtype = type[j] - 1;
fast_alpha_t& a = tabsixi[jtype];
forcelj = r6inv * (a.lj1*r6inv - a.lj2);
if (rsq > cut_lj_innersq) {
switch1 = (cut_ljsq-rsq) * (cut_ljsq-rsq) *
(tmp_coef2 + 2.0*rsq) * tmp_coef1;
switch2 = 12.0*rsq * (cut_ljsq-rsq) *
(rsq-cut_lj_innersq) * tmp_coef1;
fast_alpha_t& a = tabsixi[jtype];
philj = r6inv * (a.lj3*r6inv - a.lj4);
forcelj = forcelj*switch1 + philj*switch2;
}
}
double fpair = (forcecoul + factor_lj*forcelj) * r2inv;
tmpfx += delx*fpair;
tmpfy += dely*fpair;
tmpfz += delz*fpair;
if (NEWTON_PAIR || j < nlocal) {
ff[j].x -= delx*fpair;
ff[j].y -= dely*fpair;
ff[j].z -= delz*fpair;
}
if (EFLAG) {
if (rsq < cut_coulsq) {
if (!ncoultablebits || rsq <= tabinnersq)
ecoul = prefactor*erfc;
else {
table = etable[itable] + fraction*detable[itable];
ecoul = tmp_coef3 * table;
}
if (factor_coul < 1.0) ecoul -= (1.0-factor_coul)*prefactor;
} else ecoul = 0.0;
if (rsq < cut_ljsq) {
fast_alpha_t& a = tabsixi[jtype];
evdwl = r6inv*(a.lj3*r6inv-a.lj4);
if (rsq > cut_lj_innersq) {
switch1 = (cut_ljsq-rsq) * (cut_ljsq-rsq) *
(tmp_coef2 + 2.0*rsq) * tmp_coef1;
evdwl *= switch1;
}
evdwl *= factor_lj;
} else evdwl = 0.0;
}
if (EVFLAG) ev_tally(i,j,nlocal,NEWTON_PAIR,
evdwl,ecoul,fpair,delx,dely,delz);
}
}
}
ff[i].x += tmpfx;
ff[i].y += tmpfy;
ff[i].z += tmpfz;
}
free(fast_alpha); fast_alpha = 0;
if (vflag_fdotr) virial_fdotr_compute();
}

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