lammps/src/KSPACE/pair_coul_long.cpp

/* ----------------------------------------------------------------------
   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: Paul Crozier (SNL)
------------------------------------------------------------------------- */

#include "math.h"
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "pair_coul_long.h"
#include "atom.h"
#include "comm.h"
#include "force.h"
#include "kspace.h"
#include "neighbor.h"
#include "neigh_list.h"
#include "update.h"
#include "integrate.h"
#include "respa.h"
#include "memory.h"
#include "error.h"

using namespace LAMMPS_NS;

#define MIN(a,b) ((a) < (b) ? (a) : (b))
#define MAX(a,b) ((a) > (b) ? (a) : (b))

#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

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

PairCoulLong::PairCoulLong(LAMMPS *lmp) : Pair(lmp)
{
  ftable = NULL;
}

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

PairCoulLong::~PairCoulLong()
{
  if (allocated) {
    memory->destroy_2d_int_array(setflag);
    memory->destroy_2d_double_array(cutsq);
  }
  if (ftable) free_tables();
}

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

void PairCoulLong::compute(int eflag, int vflag)
{
  int i,j,ii,jj,inum,jnum,itable;
  double qtmp,xtmp,ytmp,ztmp,delx,dely,delz,evdwl,ecoul,fpair;
  double fraction,table;
  double r,r2inv,forcecoul,factor_coul;
  double grij,expm2,prefactor,t,erfc;
  int *ilist,*jlist,*numneigh,**firstneigh;
  float rsq;
  int *int_rsq = (int *) &rsq;

  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 nlocal = atom->nlocal;
  int nall = nlocal + atom->nghost;
  double *special_coul = force->special_coul;
  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];
    jlist = firstneigh[i];
    jnum = numneigh[i];

    for (jj = 0; jj < jnum; jj++) {
      j = jlist[jj];

      if (j < nall) factor_coul = 1.0;
      else {
	factor_coul = special_coul[j/nall];
	j %= nall;
      }

      delx = xtmp - x[j][0];
      dely = ytmp - x[j][1];
      delz = ztmp - x[j][2];
      rsq = delx*delx + dely*dely + delz*delz;

      if (rsq < cut_coulsq) {
	r2inv = 1.0/rsq;
	if (!ncoultablebits || rsq <= tabinnersq) {
	  r = sqrtf(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 {
	  itable = *int_rsq & ncoulmask;
	  itable >>= ncoulshiftbits;
	  fraction = (rsq - 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;
	  }
	}

	fpair = forcecoul * 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 (!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;
	}

	if (evflag) ev_tally(i,j,nlocal,newton_pair,
			     0.0,ecoul,fpair,delx,dely,delz);
      }
    }
  }

  if (vflag_fdotr) virial_compute();
}

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

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

  setflag = memory->create_2d_int_array(n+1,n+1,"pair:setflag");
  for (int i = 1; i <= n; i++)
    for (int j = i; j <= n; j++)
      setflag[i][j] = 0;

  cutsq = memory->create_2d_double_array(n+1,n+1,"pair:cutsq");
}

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

void PairCoulLong::settings(int narg, char **arg)
{
  if (narg != 1) error->all("Illegal pair_style command");

  cut_coul = atof(arg[0]);
}

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

void PairCoulLong::coeff(int narg, char **arg)
{
  if (narg != 2) error->all("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);

  int count = 0;
  for (int i = ilo; i <= ihi; i++) {
    for (int j = MAX(jlo,i); j <= jhi; j++) {
      setflag[i][j] = 1;
      count++;
    }
  }

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

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

void PairCoulLong::init_style()
{
  int i,j;

  if (!atom->q_flag)
    error->all("Pair style lj/cut/coul/long requires atom attribute q");

  int irequest = neighbor->request(this);

  cut_coulsq = cut_coul * cut_coul;

  // set & error check interior rRESPA cutoffs

  if (strcmp(update->integrate_style,"respa") == 0) {
    if (((Respa *) update->integrate)->level_inner >= 0) {
      cut_respa = ((Respa *) update->integrate)->cutoff;
      for (i = 1; i <= atom->ntypes; i++)
	for (j = i; j <= atom->ntypes; j++)
	  if (cut_coul < cut_respa[3])
	    error->all("Pair cutoff < Respa interior cutoff");
    }
  } else cut_respa = NULL;

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

 if (force->kspace == NULL) 
    error->all("Pair style is incompatible with KSpace style");
  g_ewald = force->kspace->g_ewald;

  // setup force tables

  if (ncoultablebits) init_tables();
}

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

double PairCoulLong::init_one(int i, int j)
{
  return cut_coul;
}

/* ----------------------------------------------------------------------
   setup force tables used in compute routines
------------------------------------------------------------------------- */

void PairCoulLong::init_tables()
{
  int masklo,maskhi;
  double r,grij,expm2,derfc,rsw;
  double qqrd2e = force->qqrd2e;

  tabinnersq = tabinner*tabinner;
  init_bitmap(tabinner,cut_coul,ncoultablebits,
	      masklo,maskhi,ncoulmask,ncoulshiftbits);
  
  int ntable = 1;
  for (int i = 0; i < ncoultablebits; i++) ntable *= 2;
  
  // linear lookup tables of length N = 2^ncoultablebits
  // stored value = value at lower edge of bin
  // d values = delta from lower edge to upper edge of bin

  if (ftable) free_tables();
  
  rtable = (double *) memory->smalloc(ntable*sizeof(double),"pair:rtable");
  ftable = (double *) memory->smalloc(ntable*sizeof(double),"pair:ftable");
  ctable = (double *) memory->smalloc(ntable*sizeof(double),"pair:ctable");
  etable = (double *) memory->smalloc(ntable*sizeof(double),"pair:etable");
  drtable = (double *) memory->smalloc(ntable*sizeof(double),"pair:drtable");
  dftable = (double *) memory->smalloc(ntable*sizeof(double),"pair:dftable");
  dctable = (double *) memory->smalloc(ntable*sizeof(double),"pair:dctable");
  detable = (double *) memory->smalloc(ntable*sizeof(double),"pair:detable");

  if (cut_respa == NULL) {
    vtable = ptable = dvtable = dptable = NULL;
  } else {
    vtable = (double *) memory->smalloc(ntable*sizeof(double),"pair:vtable");
    ptable = (double *) memory->smalloc(ntable*sizeof(double),"pair:ptable");
    dvtable = (double *) memory->smalloc(ntable*sizeof(double),"pair:dvtable");
    dptable = (double *) memory->smalloc(ntable*sizeof(double),"pair:dptable");
  }

  float rsq;
  int *int_rsq = (int *) &rsq;  
  float minrsq;
  int *int_minrsq = (int *) &minrsq;
  int itablemin;
  *int_minrsq = 0 << ncoulshiftbits;
  *int_minrsq = *int_minrsq | maskhi;
    
  for (int i = 0; i < ntable; i++) {
    *int_rsq = i << ncoulshiftbits;
    *int_rsq = *int_rsq | masklo;
    if (rsq < tabinnersq) {
      *int_rsq = i << ncoulshiftbits;
      *int_rsq = *int_rsq | maskhi;
    }
    r = sqrtf(rsq);
    grij = g_ewald * r;
    expm2 = exp(-grij*grij);
    derfc = erfc(grij);
    if (cut_respa == NULL) {
      rtable[i] = rsq;
      ftable[i] = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
      ctable[i] = qqrd2e/r;
      etable[i] = qqrd2e/r * derfc;
    } else {
      rtable[i] = rsq;
      ftable[i] = qqrd2e/r * (derfc + EWALD_F*grij*expm2 - 1.0);
      ctable[i] = 0.0;
      etable[i] = qqrd2e/r * derfc;
      ptable[i] = qqrd2e/r;
      vtable[i] = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
      if (rsq > cut_respa[2]*cut_respa[2]) {
	if (rsq < cut_respa[3]*cut_respa[3]) {
	  rsw = (r - cut_respa[2])/(cut_respa[3] - cut_respa[2]); 
	  ftable[i] += qqrd2e/r * rsw*rsw*(3.0 - 2.0*rsw);
	  ctable[i] = qqrd2e/r * rsw*rsw*(3.0 - 2.0*rsw);
	} else {
	  ftable[i] = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
	  ctable[i] = qqrd2e/r;
	}
      }
    }
    minrsq = MIN(minrsq,rsq);
  }

  tabinnersq = minrsq;
  
  int ntablem1 = ntable - 1;
  
  for (int i = 0; i < ntablem1; i++) {
    drtable[i] = 1.0/(rtable[i+1] - rtable[i]);
    dftable[i] = ftable[i+1] - ftable[i];
    dctable[i] = ctable[i+1] - ctable[i];
    detable[i] = etable[i+1] - etable[i];
  }

  if (cut_respa) {
    for (int i = 0; i < ntablem1; i++) {
      dvtable[i] = vtable[i+1] - vtable[i];
      dptable[i] = ptable[i+1] - ptable[i];
    }
  }
  
  // get the delta values for the last table entries 
  // tables are connected periodically between 0 and ntablem1
    
  drtable[ntablem1] = 1.0/(rtable[0] - rtable[ntablem1]);
  dftable[ntablem1] = ftable[0] - ftable[ntablem1];
  dctable[ntablem1] = ctable[0] - ctable[ntablem1];
  detable[ntablem1] = etable[0] - etable[ntablem1];
  if (cut_respa) {
    dvtable[ntablem1] = vtable[0] - vtable[ntablem1];
    dptable[ntablem1] = ptable[0] - ptable[ntablem1];
  }

  // get the correct delta values at itablemax    
  // smallest r is in bin itablemin
  // largest r is in bin itablemax, which is itablemin-1,
  //   or ntablem1 if itablemin=0
  // deltas at itablemax only needed if corresponding rsq < cut*cut
  // if so, compute deltas between rsq and cut*cut 
	
  double f_tmp,c_tmp,e_tmp,p_tmp,v_tmp;
  itablemin = *int_minrsq & ncoulmask;
  itablemin >>= ncoulshiftbits;  
  int itablemax = itablemin - 1; 
  if (itablemin == 0) itablemax = ntablem1;     
  *int_rsq = itablemax << ncoulshiftbits;
  *int_rsq = *int_rsq | maskhi;

  if (rsq < cut_coulsq) {
    rsq = cut_coulsq;  
    r = sqrtf(rsq);
    grij = g_ewald * r;
    expm2 = exp(-grij*grij);
    derfc = erfc(grij);

    if (cut_respa == NULL) {
      f_tmp = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
      c_tmp = qqrd2e/r;
      e_tmp = qqrd2e/r * derfc;
    } else {
      f_tmp = qqrd2e/r * (derfc + EWALD_F*grij*expm2 - 1.0);
      c_tmp = 0.0;
      e_tmp = qqrd2e/r * derfc;
      p_tmp = qqrd2e/r;
      v_tmp = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
      if (rsq > cut_respa[2]*cut_respa[2]) {
        if (rsq < cut_respa[3]*cut_respa[3]) {
          rsw = (r - cut_respa[2])/(cut_respa[3] - cut_respa[2]); 
          f_tmp += qqrd2e/r * rsw*rsw*(3.0 - 2.0*rsw);
          c_tmp = qqrd2e/r * rsw*rsw*(3.0 - 2.0*rsw);
        } else {
          f_tmp = qqrd2e/r * (derfc + EWALD_F*grij*expm2);
          c_tmp = qqrd2e/r;
        }
      }
    }

    drtable[itablemax] = 1.0/(rsq - rtable[itablemax]);   
    dftable[itablemax] = f_tmp - ftable[itablemax];
    dctable[itablemax] = c_tmp - ctable[itablemax];
    detable[itablemax] = e_tmp - etable[itablemax];
    if (cut_respa) {
      dvtable[itablemax] = v_tmp - vtable[itablemax];
      dptable[itablemax] = p_tmp - ptable[itablemax];
    }   
  }
}

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

void PairCoulLong::write_restart(FILE *fp)
{
  write_restart_settings(fp);
}

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

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

  allocate();
}

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

void PairCoulLong::write_restart_settings(FILE *fp)
{
  fwrite(&cut_coul,sizeof(double),1,fp);
  fwrite(&offset_flag,sizeof(int),1,fp);
  fwrite(&mix_flag,sizeof(int),1,fp);
}

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

void PairCoulLong::read_restart_settings(FILE *fp)
{
  if (comm->me == 0) {
    fread(&cut_coul,sizeof(double),1,fp);
    fread(&offset_flag,sizeof(int),1,fp);
    fread(&mix_flag,sizeof(int),1,fp);
  }
  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);
}

/* ----------------------------------------------------------------------
   free memory for tables used in pair computations
------------------------------------------------------------------------- */

void PairCoulLong::free_tables()
{
  memory->sfree(rtable);
  memory->sfree(drtable);
  memory->sfree(ftable);
  memory->sfree(dftable);
  memory->sfree(ctable);
  memory->sfree(dctable);
  memory->sfree(etable);
  memory->sfree(detable);
  memory->sfree(vtable);
  memory->sfree(dvtable);
  memory->sfree(ptable);
  memory->sfree(dptable);
}

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

void PairCoulLong::single(int i, int j, int itype, int jtype,
			       double rsq,
			       double factor_coul, double factor_lj,
			       int eflag, One &one)
{
  double r2inv,r,grij,expm2,t,erfc,prefactor;
  double fraction,table,forcecoul,phicoul;
  int itable;

  r2inv = 1.0/rsq;
  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 {
    float rsq_single = rsq;
    int *int_rsq = (int *) &rsq_single;
    itable = *int_rsq & ncoulmask;
    itable >>= ncoulshiftbits;
    fraction = (rsq_single - 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;
    }
  }
  one.fforce = forcecoul * r2inv;
  
  if (eflag) {
    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;
    one.eng_coul = phicoul;
    one.eng_vdwl = 0.0;
  }
}

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

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