/* ----------------------------------------------------------------------
   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: Ahmed Ismail (SNL)
------------------------------------------------------------------------- */

#include "math.h"
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "pair_born_coul_long.h"
#include "atom.h"
#include "comm.h"
#include "force.h"
#include "kspace.h"
#include "neighbor.h"
#include "neigh_list.h"
#include "math_const.h"
#include "memory.h"
#include "error.h"

using namespace LAMMPS_NS;
using namespace MathConst;

#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

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

PairBornCoulLong::PairBornCoulLong(LAMMPS *lmp) : Pair(lmp)
{
  ewaldflag = pppmflag = 1;
  ftable = NULL;
}

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

PairBornCoulLong::~PairBornCoulLong()
{
  if (allocated) {
    memory->destroy(setflag);
    memory->destroy(cutsq);

    memory->destroy(cut_lj);
    memory->destroy(cut_ljsq);
    memory->destroy(a);
    memory->destroy(rho);
    memory->destroy(sigma);
    memory->destroy(c);
    memory->destroy(d);
    memory->destroy(rhoinv);
    memory->destroy(born1);
    memory->destroy(born2);
    memory->destroy(born3);
    memory->destroy(offset);
  }
  if (ftable) free_tables();
}

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

void PairBornCoulLong::compute(int eflag, int vflag)
{
  int i,j,ii,jj,inum,jnum,itable,itype,jtype;
  double qtmp,xtmp,ytmp,ztmp,delx,dely,delz,evdwl,ecoul,fpair;
  double fraction,table;
  double rsq,r2inv,r6inv,forcecoul,forceborn,factor_coul,factor_lj;
  double grij,expm2,prefactor,t,erfc;
  double r,rexp;
  int *ilist,*jlist,*numneigh,**firstneigh;

  evdwl = ecoul = 0.0;
  if (eflag || vflag) ev_setup(eflag,vflag);
  else evflag = vflag_fdotr = 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;
  int newton_pair = force->newton_pair;
  double qqrd2e = force->qqrd2e;

  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];

    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 (!ncoultablebits || 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]) {
          r = sqrt(rsq);
          r6inv = r2inv*r2inv*r2inv;
          rexp = exp((sigma[itype][jtype]-r)*rhoinv[itype][jtype]);
          forceborn = born1[itype][jtype]*r*rexp - born2[itype][jtype]*r6inv
            + born3[itype][jtype]*r2inv*r6inv;
        } else forceborn = 0.0;

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

        f[i][0] += delx*fpair;
        f[i][1] += dely*fpair;
        f[i][2] += 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 (!ncoultablebits || 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 = a[itype][jtype]*rexp - c[itype][jtype]*r6inv
              + d[itype][jtype]*r6inv*r2inv - 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);
      }
    }
  }

  if (vflag_fdotr) virial_fdotr_compute();
}

/* ----------------------------------------------------------------------
   allocate all arrays
------------------------------------------------------------------------- */

void PairBornCoulLong::allocate()
{
  allocated = 1;
  int n = atom->ntypes;

  memory->create(setflag,n+1,n+1,"pair:setflag");
  for (int i = 1; i <= n; i++)
    for (int j = i; j <= n; j++)
      setflag[i][j] = 0;

  memory->create(cutsq,n+1,n+1,"pair:cutsq");

  memory->create(cut_lj,n+1,n+1,"pair:cut_lj");
  memory->create(cut_ljsq,n+1,n+1,"pair:cut_ljsq");
  memory->create(a,n+1,n+1,"pair:a");
  memory->create(rho,n+1,n+1,"pair:rho");
  memory->create(sigma,n+1,n+1,"pair:sigma");
  memory->create(c,n+1,n+1,"pair:c");
  memory->create(d,n+1,n+1,"pair:d");
  memory->create(rhoinv,n+1,n+1,"pair:rhoinv");
  memory->create(born1,n+1,n+1,"pair:born1");
  memory->create(born2,n+1,n+1,"pair:born2");
  memory->create(born3,n+1,n+1,"pair:born3");
  memory->create(offset,n+1,n+1,"pair:offset");
}

/* ----------------------------------------------------------------------
   global settings
------------------------------------------------------------------------- */

void PairBornCoulLong::settings(int narg, char **arg)
{
  if (narg < 1 || narg > 2) error->all(FLERR,"Illegal pair_style command");

  cut_lj_global = force->numeric(arg[0]);
  if (narg == 1) cut_coul = cut_lj_global;
  else cut_coul = force->numeric(arg[1]);

  // reset cutoffs that have been explicitly set

  if (allocated) {
    int i,j;
    for (i = 1; i <= atom->ntypes; i++)
      for (j = i+1; j <= atom->ntypes; j++)
        if (setflag[i][j]) cut_lj[i][j] = cut_lj_global;
  }
}

/* ----------------------------------------------------------------------
   set coeffs for one or more type pairs
------------------------------------------------------------------------- */

void PairBornCoulLong::coeff(int narg, char **arg)
{
  if (narg < 7 || narg > 8) error->all(FLERR,"Incorrect args for pair coefficients");
  if (!allocated) allocate();

  int ilo,ihi,jlo,jhi;
  force->bounds(arg[0],atom->ntypes,ilo,ihi);
  force->bounds(arg[1],atom->ntypes,jlo,jhi);

  double a_one = force->numeric(arg[2]);
  double rho_one = force->numeric(arg[3]);
  double sigma_one = force->numeric(arg[4]);
  if (rho_one <= 0) error->all(FLERR,"Incorrect args for pair coefficients");
  double c_one = force->numeric(arg[5]);
  double d_one = force->numeric(arg[6]);

  double cut_lj_one = cut_lj_global;
  if (narg == 8) cut_lj_one = force->numeric(arg[7]);

  int count = 0;
  for (int i = ilo; i <= ihi; i++) {
    for (int j = MAX(jlo,i); j <= jhi; j++) {
      a[i][j] = a_one;
      rho[i][j] = rho_one;
      sigma[i][j] = sigma_one;
      c[i][j] = c_one;
      d[i][j] = d_one;
      cut_lj[i][j] = cut_lj_one;
      setflag[i][j] = 1;
      count++;
    }
  }

  if (count == 0) error->all(FLERR,"Incorrect args for pair coefficients");
}

/* ----------------------------------------------------------------------
   init for one type pair i,j and corresponding j,i
------------------------------------------------------------------------- */

double PairBornCoulLong::init_one(int i, int j)
{
  if (setflag[i][j] == 0) error->all(FLERR,"All pair coeffs are not set");

  double cut = MAX(cut_lj[i][j],cut_coul);
  cut_ljsq[i][j] = cut_lj[i][j] * cut_lj[i][j];

  rhoinv[i][j] = 1.0/rho[i][j];
  born1[i][j] = a[i][j]/rho[i][j];
  born2[i][j] = 6.0*c[i][j];
  born3[i][j] = 8.0*d[i][j];

  if (offset_flag) {
    double rexp = exp((sigma[i][j]-cut_lj[i][j])*rhoinv[i][j]);
    offset[i][j] = a[i][j]*rexp - c[i][j]/pow(cut_lj[i][j],6.0) +
      d[i][j]/pow(cut_lj[i][j],8.0);
  } else offset[i][j] = 0.0;

  cut_ljsq[j][i] = cut_ljsq[i][j];
  a[j][i] = a[i][j];
  c[j][i] = c[i][j];
  d[j][i] = d[i][j];
  rhoinv[j][i] = rhoinv[i][j];
  sigma[j][i] = sigma[i][j];
  born1[j][i] = born1[i][j];
  born2[j][i] = born2[i][j];
  born3[j][i] = born3[i][j];
  offset[j][i] = offset[i][j];

  // compute I,J contribution to long-range tail correction
  // count total # of atoms of type I and J via Allreduce

  if (tail_flag) {
     int *type = atom->type;
     int nlocal = atom->nlocal;

     double count[2],all[2];
     count[0] = count[1] = 0.0;
     for (int k = 0; k < nlocal; k++) {
       if (type[k] == i) count[0] += 1.0;
       if (type[k] == j) count[1] += 1.0;
     }
     MPI_Allreduce(count,all,2,MPI_DOUBLE,MPI_SUM,world);

     double rho1 = rho[i][j];
     double rho2 = rho1*rho1;
     double rho3 = rho2*rho1;
     double rc = cut_lj[i][j];
     double rc2 = rc*rc;
     double rc3 = rc2*rc;
     double rc5 = rc3*rc2;
     etail_ij = 2.0*MY_PI*all[0]*all[1] *
       (a[i][j]*exp((sigma[i][j]-rc)/rho1)*rho1*
        (rc2 + 2.0*rho1*rc + 2.0*rho2) -
        c[i][j]/(3.0*rc3) + d[i][j]/(5.0*rc5));
     ptail_ij = (-1/3.0)*2.0*MY_PI*all[0]*all[1] *
       (-a[i][j]*exp((sigma[i][j]-rc)/rho1) *
        (rc3 + 3.0*rho1*rc2 + 6.0*rho2*rc + 6.0*rho3) +
        2.0*c[i][j]/rc3 - 8.0*d[i][j]/(5.0*rc5));
   }

  return cut;
}

/* ----------------------------------------------------------------------
   init specific to this pair style
------------------------------------------------------------------------- */

void PairBornCoulLong::init_style()
{
  if (!atom->q_flag)
    error->all(FLERR,"Pair style born/coul/long requires atom attribute q");

  cut_coulsq = cut_coul * cut_coul;

  // insure use of KSpace long-range solver, set g_ewald

  if (force->kspace == NULL)
    error->all(FLERR,"Pair style requires a KSpace style");
  g_ewald = force->kspace->g_ewald;

  neighbor->request(this);
  
  // setup force tables
  if (ncoultablebits) init_tables(cut_coul,cut_respa);
}

/* ----------------------------------------------------------------------
  proc 0 writes to restart file
------------------------------------------------------------------------- */

void PairBornCoulLong::write_restart(FILE *fp)
{
  write_restart_settings(fp);

  int i,j;
  for (i = 1; i <= atom->ntypes; i++)
    for (j = i; j <= atom->ntypes; j++) {
      fwrite(&setflag[i][j],sizeof(int),1,fp);
      if (setflag[i][j]) {
        fwrite(&a[i][j],sizeof(double),1,fp);
        fwrite(&rho[i][j],sizeof(double),1,fp);
        fwrite(&sigma[i][j],sizeof(double),1,fp);
        fwrite(&c[i][j],sizeof(double),1,fp);
        fwrite(&d[i][j],sizeof(double),1,fp);
        fwrite(&cut_lj[i][j],sizeof(double),1,fp);
      }
    }
}

/* ----------------------------------------------------------------------
  proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */

void PairBornCoulLong::read_restart(FILE *fp)
{
  read_restart_settings(fp);

  allocate();

  int i,j;
  int me = comm->me;
  for (i = 1; i <= atom->ntypes; i++)
    for (j = i; j <= atom->ntypes; j++) {
      if (me == 0) fread(&setflag[i][j],sizeof(int),1,fp);
      MPI_Bcast(&setflag[i][j],1,MPI_INT,0,world);
      if (setflag[i][j]) {
        if (me == 0) {
          fread(&a[i][j],sizeof(double),1,fp);
          fread(&rho[i][j],sizeof(double),1,fp);
          fread(&sigma[i][j],sizeof(double),1,fp);
          fread(&c[i][j],sizeof(double),1,fp);
          fread(&d[i][j],sizeof(double),1,fp);
          fread(&cut_lj[i][j],sizeof(double),1,fp);
        }
        MPI_Bcast(&a[i][j],1,MPI_DOUBLE,0,world);
        MPI_Bcast(&rho[i][j],1,MPI_DOUBLE,0,world);
        MPI_Bcast(&sigma[i][j],1,MPI_DOUBLE,0,world);
        MPI_Bcast(&c[i][j],1,MPI_DOUBLE,0,world);
        MPI_Bcast(&d[i][j],1,MPI_DOUBLE,0,world);
        MPI_Bcast(&cut_lj[i][j],1,MPI_DOUBLE,0,world);
      }
    }
}

/* ----------------------------------------------------------------------
  proc 0 writes to restart file
------------------------------------------------------------------------- */

void PairBornCoulLong::write_restart_settings(FILE *fp)
{
  fwrite(&cut_lj_global,sizeof(double),1,fp);
  fwrite(&cut_coul,sizeof(double),1,fp);
  fwrite(&offset_flag,sizeof(int),1,fp);
  fwrite(&mix_flag,sizeof(int),1,fp);
  fwrite(&tail_flag,sizeof(int),1,fp);
  fwrite(&ncoultablebits,sizeof(int),1,fp);
  fwrite(&tabinner,sizeof(double),1,fp);
}

/* ----------------------------------------------------------------------
  proc 0 reads from restart file, bcasts
------------------------------------------------------------------------- */

void PairBornCoulLong::read_restart_settings(FILE *fp)
{
  if (comm->me == 0) {
    fread(&cut_lj_global,sizeof(double),1,fp);
    fread(&cut_coul,sizeof(double),1,fp);
    fread(&offset_flag,sizeof(int),1,fp);
    fread(&mix_flag,sizeof(int),1,fp);
    fread(&tail_flag,sizeof(int),1,fp);
    fread(&ncoultablebits,sizeof(int),1,fp);
    fread(&tabinner,sizeof(double),1,fp);
  }
  MPI_Bcast(&cut_lj_global,1,MPI_DOUBLE,0,world);
  MPI_Bcast(&cut_coul,1,MPI_DOUBLE,0,world);
  MPI_Bcast(&offset_flag,1,MPI_INT,0,world);
  MPI_Bcast(&mix_flag,1,MPI_INT,0,world);
  MPI_Bcast(&tail_flag,1,MPI_INT,0,world);
  MPI_Bcast(&ncoultablebits,1,MPI_INT,0,world);
  MPI_Bcast(&tabinner,1,MPI_DOUBLE,0,world);
}

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

double PairBornCoulLong::single(int i, int j, int itype, int jtype,
                                double rsq,
                                double factor_coul, double factor_lj,
                                double &fforce)
{
  double r2inv,r6inv,r,rexp,grij,expm2,t,erfc,prefactor;
  double fraction,table,forcecoul,forceborn,phicoul,phiborn;
  int itable;

  r2inv = 1.0/rsq;
  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 * (A1+t*(A2+t*(A3+t*(A4+t*A5)))) * expm2;
      prefactor = force->qqrd2e * atom->q[i]*atom->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 = atom->q[i]*atom->q[j] * table;
      if (factor_coul < 1.0) {
        table = ctable[itable] + fraction*dctable[itable];
        prefactor = atom->q[i]*atom->q[j] * table;
        forcecoul -= (1.0-factor_coul)*prefactor;
      }
    }
  } else forcecoul = 0.0;
  if (rsq < cut_ljsq[itype][jtype]) {
    r6inv = r2inv*r2inv*r2inv;
    r = sqrt(rsq);
    rexp = exp((sigma[itype][jtype]-r)*rhoinv[itype][jtype]);
    forceborn = born1[itype][jtype]*r*rexp - born2[itype][jtype]*r6inv +
      born3[itype][jtype]*r2inv*r6inv;
  } else forceborn = 0.0;
  fforce = (forcecoul + factor_lj*forceborn) * r2inv;

  double eng = 0.0;
  if (rsq < cut_coulsq) {
    if (!ncoultablebits || rsq <= tabinnersq)
      phicoul = prefactor*erfc;
    else {
      table = etable[itable] + fraction*detable[itable];
      phicoul = atom->q[i]*atom->q[j] * table;
    }
    if (factor_coul < 1.0) phicoul -= (1.0-factor_coul)*prefactor;
    eng += phicoul;
  }
  if (rsq < cut_ljsq[itype][jtype]) {
    phiborn = a[itype][jtype]*rexp - c[itype][jtype]*r6inv +
      d[itype][jtype]*r2inv*r6inv - offset[itype][jtype];
    eng += factor_lj*phiborn;
  }
  return eng;
}

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

void *PairBornCoulLong::extract(const char *str, int &dim)
{
  dim = 0;
  if (strcmp(str,"cut_coul") == 0) return (void *) &cut_coul;
  return NULL;
}