/* ----------------------------------------------------------------------
   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 "pair_lj_cut_coul_long_opt.h"
#include <cmath>
#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 A1        0.254829592
#define A2       -0.284496736
#define A3        1.421413741
#define A4       -1.453152027
#define A5        1.061405429

/* ---------------------------------------------------------------------- */

PairLJCutCoulLongOpt::PairLJCutCoulLongOpt(LAMMPS *lmp) : PairLJCutCoulLong(lmp)
{
  respa_enable = 0;
}

/* ---------------------------------------------------------------------- */

void PairLJCutCoulLongOpt::compute(int eflag, int vflag)
{
  ev_init(eflag,vflag);

  if (!ncoultablebits) {
    if (evflag) {
      if (eflag) {
        if (force->newton_pair) return eval<1,1,1,0>();
        else return eval<1,1,0,0>();
      } else {
        if (force->newton_pair) return eval<1,0,1,0>();
        else return eval<1,0,0,0>();
      }
    } else {
      if (force->newton_pair) return eval<0,0,1,0>();
      else return eval<0,0,0,0>();
    }
  } else {
    if (evflag) {
      if (eflag) {
        if (force->newton_pair) return eval<1,1,1,1>();
        else return eval<1,1,0,1>();
      } else {
        if (force->newton_pair) return eval<1,0,1,1>();
        else return eval<1,0,0,1>();
      }
    } else {
      if (force->newton_pair) return eval<0,0,1,1>();
      else return eval<0,0,0,1>();
    }
  }
}


template < const int EVFLAG, const int EFLAG,
           const int NEWTON_PAIR, const int CTABLE >
void PairLJCutCoulLongOpt::eval()
{
  int i,ii,j,jj,inum,jnum,itype,jtype,itable;
  double qtmp,xtmp,ytmp,ztmp,delx,dely,delz,evdwl,ecoul,fpair;
  double fraction,table;
  double r,r2inv,r6inv,forcecoul,forcelj,factor_coul,factor_lj;
  double grij,expm2,prefactor,t,erfc;
  int *ilist,*jlist,*numneigh,**firstneigh;
  double rsq;

  evdwl = ecoul = 0.0;

  double **x = atom->x;
  double **f = atom->f;
  double *q = atom->q;
  int *type = atom->type;
  int nlocal = atom->nlocal;
  double *special_coul = force->special_coul;
  double *special_lj = force->special_lj;
  double qqrd2e = force->qqrd2e;
  double fxtmp,fytmp,fztmp;

  inum = list->inum;
  ilist = list->ilist;
  numneigh = list->numneigh;
  firstneigh = list->firstneigh;

  // loop over neighbors of my atoms

  for (ii = 0; ii < inum; ii++) {
    i = ilist[ii];
    qtmp = q[i];
    xtmp = x[i][0];
    ytmp = x[i][1];
    ztmp = x[i][2];
    itype = type[i];
    jlist = firstneigh[i];
    jnum = numneigh[i];
    fxtmp = fytmp = fztmp = 0.0;

    for (jj = 0; jj < jnum; jj++) {
      j = jlist[jj];
      factor_lj = special_lj[sbmask(j)];
      factor_coul = special_coul[sbmask(j)];
      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]) {
        r2inv = 1.0/rsq;

        if (rsq < cut_coulsq) {
          if (!CTABLE || rsq <= tabinnersq) {
            r = sqrt(rsq);
            grij = g_ewald * r;
            expm2 = exp(-grij*grij);
            t = 1.0 / (1.0 + EWALD_P*grij);
            erfc = t * (A1+t*(A2+t*(A3+t*(A4+t*A5)))) * expm2;
            prefactor = qqrd2e * qtmp*q[j]/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 = qtmp*q[j] * table;
            if (factor_coul < 1.0) {
              table = ctable[itable] + fraction*dctable[itable];
              prefactor = qtmp*q[j] * table;
              forcecoul -= (1.0-factor_coul)*prefactor;
            }
          }
        } else forcecoul = 0.0;

        if (rsq < cut_ljsq[itype][jtype]) {
          r6inv = r2inv*r2inv*r2inv;
          forcelj = r6inv * (lj1[itype][jtype]*r6inv - lj2[itype][jtype]);
        } else forcelj = 0.0;

        fpair = (forcecoul + factor_lj*forcelj) * r2inv;

        fxtmp += delx*fpair;
        fytmp += dely*fpair;
        fztmp += delz*fpair;
        if (NEWTON_PAIR || j < nlocal) {
          f[j][0] -= delx*fpair;
          f[j][1] -= dely*fpair;
          f[j][2] -= delz*fpair;
        }

        if (EFLAG) {
          if (rsq < cut_coulsq) {
            if (!CTABLE || rsq <= tabinnersq)
              ecoul = prefactor*erfc;
            else {
              table = etable[itable] + fraction*detable[itable];
              ecoul = qtmp*q[j] * table;
            }
            if (factor_coul < 1.0) ecoul -= (1.0-factor_coul)*prefactor;
          } else ecoul = 0.0;

          if (rsq < cut_ljsq[itype][jtype]) {
            evdwl = r6inv*(lj3[itype][jtype]*r6inv-lj4[itype][jtype]) -
              offset[itype][jtype];
            evdwl *= factor_lj;
          } else evdwl = 0.0;
        }

        if (EVFLAG) ev_tally(i,j,nlocal,NEWTON_PAIR,
                             evdwl,ecoul,fpair,delx,dely,delz);
      }
    }
    f[i][0] += fxtmp;
    f[i][1] += fytmp;
    f[i][2] += fztmp;
  }

  if (vflag_fdotr) virial_fdotr_compute();
}

/* ---------------------------------------------------------------------- */
