/* ----------------------------------------------------------------------
   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: Luca Ferraro (CASPUR)
   email: luca.ferraro@caspur.it

   Environment Dependent Interatomic Potential
   References:
    1) J. F. Justo, M. Z. Bazant, E. Kaxiras, V. V. Bulatov, S. Yip
       Phys. Rev. B 58, 2539 (1998)
------------------------------------------------------------------------- */

#include "pair_edip.h"
#include <mpi.h>
#include <cmath>
#include <cfloat>
#include <cstdlib>
#include <cstring>
#include "atom.h"
#include "neighbor.h"
#include "neigh_list.h"
#include "neigh_request.h"
#include "force.h"
#include "comm.h"
#include "memory.h"
#include "error.h"
#include "utils.h"

using namespace LAMMPS_NS;

#define MAXLINE 1024
#define DELTA 4

#define GRIDDENSITY 8000
#define GRIDSTART 0.1

// max number of interaction per atom for f(Z) environment potential

#define leadDimInteractionList 64

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

PairEDIP::PairEDIP(LAMMPS *lmp) : Pair(lmp)
{
  single_enable = 0;
  restartinfo = 0;
  one_coeff = 1;
  manybody_flag = 1;

  nelements = 0;
  elements = NULL;
  nparams = maxparam = 0;
  params = NULL;
  elem2param = NULL;
}

/* ----------------------------------------------------------------------
   check if allocated, since class can be destructed when incomplete
------------------------------------------------------------------------- */

PairEDIP::~PairEDIP()
{
  if (elements)
    for (int i = 0; i < nelements; i++) delete [] elements[i];
  delete [] elements;
  memory->destroy(params);
  memory->destroy(elem2param);

  if (allocated) {
    memory->destroy(setflag);
    memory->destroy(cutsq);
    delete [] map;

    deallocateGrids();
    deallocatePreLoops();
  }
}

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

void PairEDIP::compute(int eflag, int vflag)
{
  int i,j,k,ii,inum,jnum;
  int itype,jtype,ktype,ijparam,ikparam;
  double xtmp,ytmp,ztmp,evdwl;
  int *ilist,*jlist,*numneigh,**firstneigh;
  int preForceCoord_counter;

  double invR_ij;
  double invR_ik;
  double directorCos_ij_x;
  double directorCos_ij_y;
  double directorCos_ij_z;
  double directorCos_ik_x;
  double directorCos_ik_y;
  double directorCos_ik_z;
  double cosTeta;

  int interpolIDX;
  double interpolTMP;
  double interpolDeltaX;
  double interpolY1;
  double interpolY2;

  double invRMinusCutoffA;
  double sigmaInvRMinusCutoffA;
  double gammInvRMinusCutoffA;
  double cosTetaDiff;
  double cosTetaDiffCosTetaDiff;
  double cutoffFunction_ij;
  double exp2B_ij;
  double exp2BDerived_ij;
  double pow2B_ij;
  double pow2BDerived_ij;
  double exp3B_ij;
  double exp3BDerived_ij;
  double exp3B_ik;
  double exp3BDerived_ik;
  double qFunction;
  double tauFunction;
  double tauFunctionDerived;
  double expMinusBetaZeta_iZeta_i;
  double qFunctionCosTetaDiffCosTetaDiff;
  double expMinusQFunctionCosTetaDiffCosTetaDiff;
  double zeta_i;
  double zeta_iDerived;
  double zeta_iDerivedInvR_ij;

  double forceModCoord_factor;
  double forceModCoord;
  double forceModCoord_ij;
  double forceMod2B;
  double forceMod3B_factor1_ij;
  double forceMod3B_factor2_ij;
  double forceMod3B_factor2;
  double forceMod3B_factor1_ik;
  double forceMod3B_factor2_ik;
  double potentia3B_factor;
  double potential2B_factor;

  evdwl = 0.0;
  ev_init(eflag,vflag);

  double **x = atom->x;
  double **f = atom->f;
  int *type = atom->type;
  int nlocal = atom->nlocal;
  int newton_pair = force->newton_pair;

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

  // loop over full neighbor list of my atoms

  for (ii = 0; ii < inum; ii++) {
    zeta_i = 0.0;
    int numForceCoordPairs = 0;

    i = ilist[ii];
    itype = map[type[i]];
    xtmp = x[i][0];
    ytmp = x[i][1];
    ztmp = x[i][2];

    jlist = firstneigh[i];
    jnum = numneigh[i];

    // pre-loop to compute environment coordination f(Z)

    for (int neighbor_j = 0; neighbor_j < jnum; neighbor_j++) {
        j = jlist[neighbor_j];
        j &= NEIGHMASK;

        double dr_ij[3], r_ij;

        dr_ij[0] = xtmp - x[j][0];
        dr_ij[1] = ytmp - x[j][1];
        dr_ij[2] = ztmp - x[j][2];
        r_ij = dr_ij[0]*dr_ij[0] + dr_ij[1]*dr_ij[1] + dr_ij[2]*dr_ij[2];

        jtype = map[type[j]];
        ijparam = elem2param[itype][jtype][jtype];
        if (r_ij > params[ijparam].cutsq) continue;

        r_ij = sqrt(r_ij);

        invR_ij = 1.0 / r_ij;
        preInvR_ij[neighbor_j] = invR_ij;

        invRMinusCutoffA =  1.0 / (r_ij - cutoffA);
        sigmaInvRMinusCutoffA = sigma * invRMinusCutoffA;
        gammInvRMinusCutoffA = gamm * invRMinusCutoffA;

        interpolDeltaX = r_ij - GRIDSTART;
        interpolTMP = (interpolDeltaX * GRIDDENSITY);
        interpolIDX = (int) interpolTMP;

        interpolY1 = exp3B[interpolIDX];
        interpolY2 = exp3B[interpolIDX+1];
        exp3B_ij = interpolY1 + (interpolY2 - interpolY1) *
          (interpolTMP-interpolIDX);

        exp3BDerived_ij = - exp3B_ij * gammInvRMinusCutoffA * invRMinusCutoffA;

        preExp3B_ij[neighbor_j] = exp3B_ij;
        preExp3BDerived_ij[neighbor_j] = exp3BDerived_ij;

        interpolY1 = exp2B[interpolIDX];
        interpolY2 = exp2B[interpolIDX+1];
        exp2B_ij = interpolY1 + (interpolY2 - interpolY1) *
          (interpolTMP-interpolIDX);

        exp2BDerived_ij = - exp2B_ij * sigmaInvRMinusCutoffA * invRMinusCutoffA;

        preExp2B_ij[neighbor_j] = exp2B_ij;
        preExp2BDerived_ij[neighbor_j] = exp2BDerived_ij;

        interpolY1 = pow2B[interpolIDX];
        interpolY2 = pow2B[interpolIDX+1];
        pow2B_ij = interpolY1 + (interpolY2 - interpolY1) *
          (interpolTMP-interpolIDX);

        prePow2B_ij[neighbor_j] = pow2B_ij;

        // zeta and its derivative

        if (r_ij < cutoffC) zeta_i += 1.0;
        else {
            interpolY1 = cutoffFunction[interpolIDX];
            interpolY2 = cutoffFunction[interpolIDX+1];
            cutoffFunction_ij = interpolY1 + (interpolY2 - interpolY1) *
              (interpolTMP-interpolIDX);

            zeta_i += cutoffFunction_ij;

            interpolY1 = cutoffFunctionDerived[interpolIDX];
            interpolY2 = cutoffFunctionDerived[interpolIDX+1];
            zeta_iDerived = interpolY1 + (interpolY2 - interpolY1) *
              (interpolTMP-interpolIDX);

            zeta_iDerivedInvR_ij = zeta_iDerived * invR_ij;

            preForceCoord_counter=numForceCoordPairs*5;
            preForceCoord[preForceCoord_counter+0]=zeta_iDerivedInvR_ij;
            preForceCoord[preForceCoord_counter+1]=dr_ij[0];
            preForceCoord[preForceCoord_counter+2]=dr_ij[1];
            preForceCoord[preForceCoord_counter+3]=dr_ij[2];
            preForceCoord[preForceCoord_counter+4]=j;
            numForceCoordPairs++;
        }
    }

    // quantities depending on zeta_i

    interpolDeltaX = zeta_i;
    interpolTMP = (interpolDeltaX * GRIDDENSITY);
    interpolIDX = (int) interpolTMP;

    interpolY1 = expMinusBetaZeta_iZeta_iGrid[interpolIDX];
    interpolY2 = expMinusBetaZeta_iZeta_iGrid[interpolIDX+1];
    expMinusBetaZeta_iZeta_i = interpolY1 + (interpolY2 - interpolY1) *
      (interpolTMP-interpolIDX);

    interpolY1 = qFunctionGrid[interpolIDX];
    interpolY2 = qFunctionGrid[interpolIDX+1];
    qFunction = interpolY1 + (interpolY2 - interpolY1) *
      (interpolTMP-interpolIDX);

    interpolY1 = tauFunctionGrid[interpolIDX];
    interpolY2 = tauFunctionGrid[interpolIDX+1];
    tauFunction = interpolY1 + (interpolY2 - interpolY1) *
      (interpolTMP-interpolIDX);

    interpolY1 = tauFunctionDerivedGrid[interpolIDX];
    interpolY2 = tauFunctionDerivedGrid[interpolIDX+1];
    tauFunctionDerived = interpolY1 + (interpolY2 - interpolY1) *
      (interpolTMP-interpolIDX);

    forceModCoord_factor = 2.0 * beta * zeta_i * expMinusBetaZeta_iZeta_i;

    forceModCoord = 0.0;

    // two-body interactions, skip half of them

    for (int neighbor_j = 0; neighbor_j < jnum; neighbor_j++) {
      double dr_ij[3], r_ij, f_ij[3];

      j = jlist[neighbor_j];
      j &= NEIGHMASK;

      dr_ij[0] = x[j][0] - xtmp;
      dr_ij[1] = x[j][1] - ytmp;
      dr_ij[2] = x[j][2] - ztmp;
      r_ij = dr_ij[0]*dr_ij[0] + dr_ij[1]*dr_ij[1] + dr_ij[2]*dr_ij[2];

      jtype = map[type[j]];
      ijparam = elem2param[itype][jtype][jtype];
      if (r_ij > params[ijparam].cutsq) continue;

      r_ij = sqrt(r_ij);

      invR_ij = preInvR_ij[neighbor_j];
      pow2B_ij = prePow2B_ij[neighbor_j];

      potential2B_factor = pow2B_ij - expMinusBetaZeta_iZeta_i;

      exp2B_ij = preExp2B_ij[neighbor_j];

      pow2BDerived_ij = - rho * invR_ij * pow2B_ij;

      forceModCoord += (forceModCoord_factor*exp2B_ij);

      exp2BDerived_ij = preExp2BDerived_ij[neighbor_j];
      forceMod2B = exp2BDerived_ij * potential2B_factor +
        exp2B_ij * pow2BDerived_ij;

      directorCos_ij_x = invR_ij * dr_ij[0];
      directorCos_ij_y = invR_ij * dr_ij[1];
      directorCos_ij_z = invR_ij * dr_ij[2];

      exp3B_ij = preExp3B_ij[neighbor_j];
      exp3BDerived_ij = preExp3BDerived_ij[neighbor_j];

      f_ij[0] = forceMod2B * directorCos_ij_x;
      f_ij[1] = forceMod2B * directorCos_ij_y;
      f_ij[2] = forceMod2B * directorCos_ij_z;

      f[i][0] += f_ij[0];
      f[i][1] += f_ij[1];
      f[i][2] += f_ij[2];

      f[j][0] -= f_ij[0];
      f[j][1] -= f_ij[1];
      f[j][2] -= f_ij[2];

      // potential energy

      evdwl = (exp2B_ij * potential2B_factor);

      if (evflag) ev_tally(i, j, nlocal, newton_pair, evdwl, 0.0,
                           -forceMod2B*invR_ij, dr_ij[0], dr_ij[1], dr_ij[2]);

      // three-body Forces

      for (int neighbor_k = neighbor_j + 1; neighbor_k < jnum; neighbor_k++) {
          double dr_ik[3], r_ik, f_ik[3];

          k = jlist[neighbor_k];
          k &= NEIGHMASK;
          ktype = map[type[k]];
          ikparam = elem2param[itype][ktype][ktype];

          dr_ik[0] = x[k][0] - xtmp;
          dr_ik[1] = x[k][1] - ytmp;
          dr_ik[2] = x[k][2] - ztmp;
          r_ik = dr_ik[0]*dr_ik[0] + dr_ik[1]*dr_ik[1] + dr_ik[2]*dr_ik[2];

          if (r_ik > params[ikparam].cutsq) continue;

          r_ik = sqrt(r_ik);

          invR_ik = preInvR_ij[neighbor_k];

          directorCos_ik_x = invR_ik * dr_ik[0];
          directorCos_ik_y = invR_ik * dr_ik[1];
          directorCos_ik_z = invR_ik * dr_ik[2];

          cosTeta = directorCos_ij_x * directorCos_ik_x +
            directorCos_ij_y * directorCos_ik_y +
            directorCos_ij_z * directorCos_ik_z;

          cosTetaDiff = cosTeta + tauFunction;
          cosTetaDiffCosTetaDiff = cosTetaDiff * cosTetaDiff;
          qFunctionCosTetaDiffCosTetaDiff = cosTetaDiffCosTetaDiff * qFunction;
          expMinusQFunctionCosTetaDiffCosTetaDiff =
            exp(-qFunctionCosTetaDiffCosTetaDiff);

          potentia3B_factor = lambda *
            ((1.0 - expMinusQFunctionCosTetaDiffCosTetaDiff) +
             eta * qFunctionCosTetaDiffCosTetaDiff);

          exp3B_ik = preExp3B_ij[neighbor_k];
          exp3BDerived_ik = preExp3BDerived_ij[neighbor_k];

          forceMod3B_factor1_ij = - exp3BDerived_ij * exp3B_ik *
            potentia3B_factor;
          forceMod3B_factor2 = 2.0 * lambda * exp3B_ij * exp3B_ik *
            qFunction * cosTetaDiff *
            (eta + expMinusQFunctionCosTetaDiffCosTetaDiff);
          forceMod3B_factor2_ij = forceMod3B_factor2 * invR_ij;

          f_ij[0] = forceMod3B_factor1_ij * directorCos_ij_x +
            forceMod3B_factor2_ij *
            (cosTeta * directorCos_ij_x - directorCos_ik_x);
          f_ij[1] = forceMod3B_factor1_ij * directorCos_ij_y +
            forceMod3B_factor2_ij *
            (cosTeta * directorCos_ij_y - directorCos_ik_y);
          f_ij[2] = forceMod3B_factor1_ij * directorCos_ij_z +
            forceMod3B_factor2_ij *
            (cosTeta * directorCos_ij_z - directorCos_ik_z);

          forceMod3B_factor1_ik = - exp3BDerived_ik * exp3B_ij *
            potentia3B_factor;
          forceMod3B_factor2_ik = forceMod3B_factor2 * invR_ik;

          f_ik[0] = forceMod3B_factor1_ik * directorCos_ik_x +
            forceMod3B_factor2_ik *
            (cosTeta * directorCos_ik_x - directorCos_ij_x);
          f_ik[1] = forceMod3B_factor1_ik * directorCos_ik_y +
            forceMod3B_factor2_ik *
            (cosTeta * directorCos_ik_y - directorCos_ij_y);
          f_ik[2] = forceMod3B_factor1_ik * directorCos_ik_z +
            forceMod3B_factor2_ik *
            (cosTeta * directorCos_ik_z - directorCos_ij_z);

          forceModCoord += (forceMod3B_factor2 *
                            (tauFunctionDerived -  0.5 * mu * cosTetaDiff));

          f[j][0] += f_ij[0];
          f[j][1] += f_ij[1];
          f[j][2] += f_ij[2];

          f[k][0] += f_ik[0];
          f[k][1] += f_ik[1];
          f[k][2] += f_ik[2];

          f[i][0] -= f_ij[0] + f_ik[0];
          f[i][1] -= f_ij[1] + f_ik[1];
          f[i][2] -= f_ij[2] + f_ik[2];

          // potential energy

          evdwl = (exp3B_ij * exp3B_ik * potentia3B_factor);

          if (evflag) ev_tally3(i,j,k,evdwl,0.0,f_ij,f_ik,dr_ij,dr_ik);
      }
    }

    // forces due to environment coordination f(Z)

    for (int idx = 0; idx < numForceCoordPairs; idx++) {
        double dr_ij[3],f_ij[3];

        preForceCoord_counter = idx * 5;
        zeta_iDerivedInvR_ij=preForceCoord[preForceCoord_counter+0];
        dr_ij[0]=preForceCoord[preForceCoord_counter+1];
        dr_ij[1]=preForceCoord[preForceCoord_counter+2];
        dr_ij[2]=preForceCoord[preForceCoord_counter+3];
        j = static_cast<int> (preForceCoord[preForceCoord_counter+4]);

        forceModCoord_ij = forceModCoord * zeta_iDerivedInvR_ij;

        f_ij[0] = forceModCoord_ij * dr_ij[0];
        f_ij[1] = forceModCoord_ij * dr_ij[1];
        f_ij[2] = forceModCoord_ij * dr_ij[2];

        f[i][0] -= f_ij[0];
        f[i][1] -= f_ij[1];
        f[i][2] -= f_ij[2];

        f[j][0] += f_ij[0];
        f[j][1] += f_ij[1];
        f[j][2] += f_ij[2];

        // potential energy

        evdwl = 0.0;
        if (evflag) ev_tally(i, j, nlocal, newton_pair, evdwl, 0.0,
                             -forceModCoord_ij, dr_ij[0], dr_ij[1], dr_ij[2]);
    }
  }

  if (vflag_fdotr) virial_fdotr_compute();
}

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

void PairEDIP::allocateGrids(void)
{
  int numGridPointsOneCutoffFunction;
  int numGridPointsNotOneCutoffFunction;
  int numGridPointsCutoffFunction;
  int numGridPointsR;
  int numGridPointsRTotal;
  int numGridPointsQFunctionGrid;
  int numGridPointsExpMinusBetaZeta_iZeta_i;
  int numGridPointsTauFunctionGrid;
  double maxArgumentTauFunctionGrid;
  double maxArgumentQFunctionGrid;
  double maxArgumentExpMinusBetaZeta_iZeta_i;
  double const leftLimitToZero = -DBL_MIN * 1000.0;

  // tauFunctionGrid

  maxArgumentTauFunctionGrid = leadDimInteractionList;
  numGridPointsTauFunctionGrid = (int)
    ((maxArgumentTauFunctionGrid) * GRIDDENSITY) + 2;

  memory->create(tauFunctionGrid,numGridPointsTauFunctionGrid,
                 "edip:tauFunctionGrid");
  memory->create(tauFunctionDerivedGrid,numGridPointsTauFunctionGrid,
                 "edip:tauFunctionDerivedGrid");

  // expMinusBetaZeta_iZeta_iGrid

  maxArgumentExpMinusBetaZeta_iZeta_i = leadDimInteractionList;
  numGridPointsExpMinusBetaZeta_iZeta_i = (int)
    ((maxArgumentExpMinusBetaZeta_iZeta_i) * GRIDDENSITY) + 2;
  memory->create(expMinusBetaZeta_iZeta_iGrid,
                 numGridPointsExpMinusBetaZeta_iZeta_i,
                 "edip:expMinusBetaZeta_iZeta_iGrid");

  // qFunctionGrid

  maxArgumentQFunctionGrid = leadDimInteractionList;
  numGridPointsQFunctionGrid = (int)
    ((maxArgumentQFunctionGrid) * GRIDDENSITY) + 2;
  memory->create(qFunctionGrid,numGridPointsQFunctionGrid,"edip:qFunctionGrid");

  // cutoffFunction

  numGridPointsOneCutoffFunction = (int) ((cutoffC - GRIDSTART) * GRIDDENSITY);
  numGridPointsNotOneCutoffFunction = (int) ((cutoffA-cutoffC) * GRIDDENSITY);
  numGridPointsCutoffFunction = numGridPointsOneCutoffFunction +
    numGridPointsNotOneCutoffFunction+2;

  memory->create(cutoffFunction,numGridPointsCutoffFunction,
                 "edip:cutoffFunction");
  memory->create(cutoffFunctionDerived,numGridPointsCutoffFunction,
                 "edip:cutoffFunctionDerived");

  // pow2B

  numGridPointsR = (int)
    ((cutoffA + leftLimitToZero - GRIDSTART) * GRIDDENSITY);
  numGridPointsRTotal = numGridPointsR + 2;

  memory->create(pow2B,numGridPointsRTotal,"edip:pow2B");
  memory->create(exp2B,numGridPointsRTotal,"edip:exp2B");
  memory->create(exp3B,numGridPointsRTotal,"edip:exp3B");
}

/* ----------------------------------------------------------------------
   pre-calculated structures
------------------------------------------------------------------------- */

void PairEDIP::allocatePreLoops(void)
{
  int nthreads = comm->nthreads;

  memory->create(preInvR_ij,nthreads*leadDimInteractionList,"edip:preInvR_ij");
  memory->create(preExp3B_ij,nthreads*leadDimInteractionList,"edip:preExp3B_ij");
  memory->create(preExp3BDerived_ij,nthreads*leadDimInteractionList,
                 "edip:preExp3BDerived_ij");
  memory->create(preExp2B_ij,nthreads*leadDimInteractionList,"edip:preExp2B_ij");
  memory->create(preExp2BDerived_ij,nthreads*leadDimInteractionList,
                 "edip:preExp2BDerived_ij");
  memory->create(prePow2B_ij,nthreads*leadDimInteractionList,"edip:prePow2B_ij");
  memory->create(preForceCoord,5*nthreads*leadDimInteractionList,"edip:preForceCoord");
}

/* ----------------------------------------------------------------------
   deallocate grids
------------------------------------------------------------------------- */

void PairEDIP::deallocateGrids(void)
{
  memory->destroy(cutoffFunction);
  memory->destroy(cutoffFunctionDerived);
  memory->destroy(pow2B);
  memory->destroy(exp2B);
  memory->destroy(exp3B);
  memory->destroy(qFunctionGrid);
  memory->destroy(expMinusBetaZeta_iZeta_iGrid);
  memory->destroy(tauFunctionGrid);
  memory->destroy(tauFunctionDerivedGrid);
}

/* ----------------------------------------------------------------------
   deallocate preLoops
------------------------------------------------------------------------- */

void PairEDIP::deallocatePreLoops(void)
{
  memory->destroy(preInvR_ij);
  memory->destroy(preExp3B_ij);
  memory->destroy(preExp3BDerived_ij);
  memory->destroy(preExp2B_ij);
  memory->destroy(preExp2BDerived_ij);
  memory->destroy(prePow2B_ij);
  memory->destroy(preForceCoord);
}

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

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

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

  map = new int[n+1];
}

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

void PairEDIP::settings(int narg, char **/*arg*/)
{
  if (narg != 0) error->all(FLERR,"Illegal pair_style command");
}

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

void PairEDIP::initGrids(void)
{
  int l;
  int numGridPointsOneCutoffFunction;
  int numGridPointsNotOneCutoffFunction;
  int numGridPointsCutoffFunction;
  int numGridPointsR;
  int numGridPointsQFunctionGrid;
  int numGridPointsExpMinusBetaZeta_iZeta_i;
  int numGridPointsTauFunctionGrid;
  double maxArgumentTauFunctionGrid;
  double maxArgumentQFunctionGrid;
  double maxArgumentExpMinusBetaZeta_iZeta_i;
  double r;
  double temp;
  double temp3;
  double temp4;
  double deltaArgumentR;
  double deltaArgumentCutoffFunction;
  double deltaArgumentQFunctionGrid;
  double deltaArgumentTauFunctionGrid;
  double deltaArgumentExpMinusBetaZeta_iZeta_i;
  double const leftLimitToZero = -DBL_MIN * 1000.0;

  // tauFunctionGrid

  maxArgumentTauFunctionGrid = leadDimInteractionList;

  numGridPointsTauFunctionGrid = (int)
    ((maxArgumentTauFunctionGrid) * GRIDDENSITY) + 2;

  r = 0.0;
  deltaArgumentTauFunctionGrid = 1.0 / GRIDDENSITY;

  for (l = 0; l < numGridPointsTauFunctionGrid; l++) {
      tauFunctionGrid[l] = u1 + u2 * u3 * exp(-u4 * r) -
        u2 * exp(-2.0 * u4 * r);
      tauFunctionDerivedGrid[l] = - u2 * u3 * u4 * exp(-u4 * r) +
        2.0 * u2 * u4 * exp(-2.0 * u4 * r);
      r += deltaArgumentTauFunctionGrid;
  }

  // expMinusBetaZeta_iZeta_iGrid

  maxArgumentExpMinusBetaZeta_iZeta_i = leadDimInteractionList;

  numGridPointsExpMinusBetaZeta_iZeta_i = (int)
    ((maxArgumentExpMinusBetaZeta_iZeta_i) * GRIDDENSITY) + 2;

  r = 0.0;
  deltaArgumentExpMinusBetaZeta_iZeta_i = 1.0 / GRIDDENSITY;

  for (l = 0; l < numGridPointsExpMinusBetaZeta_iZeta_i; l++) {
      expMinusBetaZeta_iZeta_iGrid[l] = exp(-beta * r * r);
      r += deltaArgumentExpMinusBetaZeta_iZeta_i;
  }

  // qFunctionGrid

  maxArgumentQFunctionGrid = leadDimInteractionList;
  numGridPointsQFunctionGrid =
    (int) ((maxArgumentQFunctionGrid) * GRIDDENSITY) + 2;

  r = 0.0;
  deltaArgumentQFunctionGrid = 1.0 / GRIDDENSITY;

  for (l = 0; l < numGridPointsQFunctionGrid; l++) {
      qFunctionGrid[l] = Q0 * exp(-mu * r);
      r += deltaArgumentQFunctionGrid;
  }

  // cutoffFunction

  numGridPointsOneCutoffFunction =
    (int) ((cutoffC - GRIDSTART) * GRIDDENSITY);
  numGridPointsNotOneCutoffFunction =
    (int) ((cutoffA-cutoffC) * GRIDDENSITY);
  numGridPointsCutoffFunction =
    numGridPointsOneCutoffFunction+numGridPointsNotOneCutoffFunction+2;

  r = GRIDSTART;
  deltaArgumentCutoffFunction = 1.0 / GRIDDENSITY;

  for (l = 0; l < numGridPointsOneCutoffFunction; l++) {
      cutoffFunction[l] = 1.0;
      cutoffFunctionDerived[l] = 0.0;
      r += deltaArgumentCutoffFunction;
  }

  for (l = numGridPointsOneCutoffFunction;
       l < numGridPointsCutoffFunction; l++) {
      temp = (cutoffA - cutoffC)/(r - cutoffC);
      temp3 = temp * temp * temp;
      temp4 = temp3 * temp;
      cutoffFunction[l] = exp(alpha/(1.0-temp3));
      cutoffFunctionDerived[l] = (-3*alpha/(cutoffA-cutoffC)) *
        (temp4/((1-temp3)*(1-temp3)))*exp(alpha/(1.0-temp3));
      r += deltaArgumentCutoffFunction;
  }

  // pow2B

  numGridPointsR = (int)
    ((cutoffA + leftLimitToZero - GRIDSTART) * GRIDDENSITY);

  r = GRIDSTART;
  deltaArgumentR = 1.0 / GRIDDENSITY;
  for (l = 0; l < numGridPointsR; l++) {
      pow2B[l] = pow((B/r),rho);
      exp2B[l] = A * exp(sigma/(r-cutoffA));
      exp3B[l] = exp(gamm/(r-cutoffA));
      r += deltaArgumentR;
  }

  pow2B[numGridPointsR] = pow((B/r),rho);
  exp2B[numGridPointsR]=0;
  exp3B[numGridPointsR]=0;
  r += deltaArgumentR;
  pow2B[numGridPointsR+1] = pow((B/r),rho);
  exp2B[numGridPointsR+1]=0;
  exp3B[numGridPointsR+1]=0;
}

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

void PairEDIP::coeff(int narg, char **arg)
{
  int i,j,n;

  if (!allocated) allocate();

  if (narg != 3 + atom->ntypes)
    error->all(FLERR,"Incorrect args for pair coefficients");

  // insure I,J args are * *

  if (strcmp(arg[0],"*") != 0 || strcmp(arg[1],"*") != 0)
    error->all(FLERR,"Incorrect args for pair coefficients");

  // read args that map atom types to elements in potential file
  // map[i] = which element the Ith atom type is, -1 if NULL
  // nelements = # of unique elements
  // elements = list of element names

  if (elements) {
    for (i = 0; i < nelements; i++) delete [] elements[i];
    delete [] elements;
  }
  elements = new char*[atom->ntypes];
  for (i = 0; i < atom->ntypes; i++) elements[i] = NULL;

  nelements = 0;
  for (i = 3; i < narg; i++) {
    if (strcmp(arg[i],"NULL") == 0) {
      map[i-2] = -1;
      continue;
    }
    for (j = 0; j < nelements; j++)
      if (strcmp(arg[i],elements[j]) == 0) break;
    map[i-2] = j;
    if (j == nelements) {
      n = strlen(arg[i]) + 1;
      elements[j] = new char[n];
      strcpy(elements[j],arg[i]);
      nelements++;
    }
  }

  if (nelements != 1)
    error->all(FLERR,"Pair style edip only supports single element potentials");

  // read potential file and initialize potential parameters

  read_file(arg[2]);
  setup_params();

  // clear setflag since coeff() called once with I,J = * *

  n = atom->ntypes;
  for (int i = 1; i <= n; i++)
    for (int j = i; j <= n; j++)
      setflag[i][j] = 0;

  // set setflag i,j for type pairs where both are mapped to elements

  int count = 0;
  for (int i = 1; i <= n; i++)
    for (int j = i; j <= n; j++)
      if (map[i] >= 0 && map[j] >= 0) {
        setflag[i][j] = 1;
        count++;
      }

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

  // allocate tables and internal structures

  allocatePreLoops();
  allocateGrids();
  initGrids();
}

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

void PairEDIP::init_style()
{
  if (force->newton_pair == 0)
    error->all(FLERR,"Pair style edip requires newton pair on");

  // need a full neighbor list

  int irequest = neighbor->request(this,instance_me);
  neighbor->requests[irequest]->half = 0;
  neighbor->requests[irequest]->full = 1;
}

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

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

  return cutmax;
}

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

void PairEDIP::read_file(char *file)
{
  int params_per_line = 20;
  char **words = new char*[params_per_line+1];

  memory->sfree(params);
  params = NULL;
  nparams = maxparam = 0;

  // open file on proc 0

  FILE *fp;
  if (comm->me == 0) {
    fp = force->open_potential(file);
    if (fp == NULL) {
      char str[128];
      snprintf(str,128,"Cannot open EDIP potential file %s",file);
      error->one(FLERR,str);
    }
  }

  // read each set of params from potential file
  // one set of params can span multiple lines
  // store params if all 3 element tags are in element list

  int n,nwords,ielement,jelement,kelement;
  char line[MAXLINE],*ptr;
  int eof = 0;

  while (1) {
    if (comm->me == 0) {
      ptr = fgets(line,MAXLINE,fp);
      if (ptr == NULL) {
        eof = 1;
        fclose(fp);
      } else n = strlen(line) + 1;
    }
    MPI_Bcast(&eof,1,MPI_INT,0,world);
    if (eof) break;
    MPI_Bcast(&n,1,MPI_INT,0,world);
    MPI_Bcast(line,n,MPI_CHAR,0,world);

    // strip comment, skip line if blank

    if ((ptr = strchr(line,'#'))) *ptr = '\0';
    nwords = utils::count_words(line);
    if (nwords == 0) continue;

    // concatenate additional lines until have params_per_line words

    while (nwords < params_per_line) {
      n = strlen(line);
      if (comm->me == 0) {
        ptr = fgets(&line[n],MAXLINE-n,fp);
        if (ptr == NULL) {
          eof = 1;
          fclose(fp);
        } else n = strlen(line) + 1;
      }
      MPI_Bcast(&eof,1,MPI_INT,0,world);
      if (eof) break;
      MPI_Bcast(&n,1,MPI_INT,0,world);
      MPI_Bcast(line,n,MPI_CHAR,0,world);
      if ((ptr = strchr(line,'#'))) *ptr = '\0';
      nwords = utils::count_words(line);
    }

    if (nwords != params_per_line)
      error->all(FLERR,"Incorrect format in EDIP potential file");

    // words = ptrs to all words in line

    nwords = 0;
    words[nwords++] = strtok(line," \t\n\r\f");
    while ((words[nwords++] = strtok(NULL," \t\n\r\f"))) continue;

    // ielement,jelement,kelement = 1st args
    // if all 3 args are in element list, then parse this line
    // else skip to next entry in file

    for (ielement = 0; ielement < nelements; ielement++)
      if (strcmp(words[0],elements[ielement]) == 0) break;
    if (ielement == nelements) continue;
    for (jelement = 0; jelement < nelements; jelement++)
      if (strcmp(words[1],elements[jelement]) == 0) break;
    if (jelement == nelements) continue;
    for (kelement = 0; kelement < nelements; kelement++)
      if (strcmp(words[2],elements[kelement]) == 0) break;
    if (kelement == nelements) continue;

    // load up parameter settings and error check their values

    if (nparams == maxparam) {
      maxparam += DELTA;
      params = (Param *) memory->srealloc(params,maxparam*sizeof(Param),
                                          "pair:params");
    }

    params[nparams].ielement = ielement;
    params[nparams].jelement = jelement;
    params[nparams].kelement = kelement;
    params[nparams].A = atof(words[3]);
    params[nparams].B = atof(words[4]);
    params[nparams].cutoffA = atof(words[5]);
    params[nparams].cutoffC = atof(words[6]);
    params[nparams].alpha = atof(words[7]);
    params[nparams].beta = atof(words[8]);
    params[nparams].eta = atof(words[9]);
    params[nparams].gamm = atof(words[10]);
    params[nparams].lambda = atof(words[11]);
    params[nparams].mu = atof(words[12]);
    params[nparams].rho = atof(words[13]);
    params[nparams].sigma = atof(words[14]);
    params[nparams].Q0 = atof(words[15]);
    params[nparams].u1 = atof(words[16]);
    params[nparams].u2 = atof(words[17]);
    params[nparams].u3 = atof(words[18]);
    params[nparams].u4 = atof(words[19]);

    if (params[nparams].A < 0.0 || params[nparams].B < 0.0 ||
        params[nparams].cutoffA < 0.0 || params[nparams].cutoffC < 0.0 ||
        params[nparams].alpha < 0.0 || params[nparams].beta < 0.0 ||
        params[nparams].eta < 0.0 || params[nparams].gamm < 0.0 ||
        params[nparams].lambda < 0.0 || params[nparams].mu < 0.0 ||
        params[nparams].rho < 0.0 || params[nparams].sigma < 0.0)
      error->all(FLERR,"Illegal EDIP parameter");

    nparams++;
  }

  delete [] words;
}

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

void PairEDIP::setup_params()
{
  int i,j,k,m,n;
  double rtmp;

  // set elem2param for all triplet combinations
  // must be a single exact match to lines read from file
  // do not allow for ACB in place of ABC

  memory->destroy(elem2param);
  memory->create(elem2param,nelements,nelements,nelements,"pair:elem2param");

  for (i = 0; i < nelements; i++)
    for (j = 0; j < nelements; j++)
      for (k = 0; k < nelements; k++) {
        n = -1;
        for (m = 0; m < nparams; m++) {
          if (i == params[m].ielement && j == params[m].jelement &&
              k == params[m].kelement) {
            if (n >= 0) error->all(FLERR,"Potential file has duplicate entry");
            n = m;
          }
        }
        if (n < 0) error->all(FLERR,"Potential file is missing an entry");
        elem2param[i][j][k] = n;
      }

  // set cutoff square

  for (m = 0; m < nparams; m++) {
    params[m].cutsq = params[m].cutoffA*params[m].cutoffA;
  }

  // set cutmax to max of all params

  cutmax = 0.0;
  for (m = 0; m < nparams; m++) {
    rtmp = sqrt(params[m].cutsq);
    if (rtmp > cutmax) cutmax = rtmp;
  }

  // this should be removed for multi species parameterization

  A = params[0].A;
  B = params[0].B;
  rho = params[0].rho;
  cutoffA = params[0].cutoffA;
  cutoffC = params[0].cutoffC;
  sigma = params[0].sigma;
  lambda = params[0].lambda;
  gamm = params[0].gamm;
  eta = params[0].eta;
  Q0 = params[0].Q0;
  mu = params[0].mu;
  beta = params[0].beta;
  alpha = params[0].alpha;
  u1 = params[0].u1;
  u2 = params[0].u2;
  u3 = params[0].u3;
  u4 = params[0].u4;
}
