pair_cdeam.cpp
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Created: Tue, Nov 5, 20:10

pair_cdeam.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 author: Alexander Stukowski
	Technical University of Darmstadt,
	Germany Department of Materials Science
	------------------------------------------------------------------------- */

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

	using namespace LAMMPS_NS;

	// This is for debugging purposes. The ASSERT() macro is used in the code to check
	// if everything runs as expected. Change this to #if 0 if you don't need the checking.
	#if 0
	#define ASSERT(cond) ((!(cond)) ? my_failure(error,__FILE__,__LINE__) : my_noop())

	inline void my_noop() {}
	inline void my_failure(Error* error, const char* file, int line) {
	char str[1024];
	sprintf(str,"Assertion failure: File %s, line %i", file, line);
	error->one(FLERR,str);
	}
	#else
	#define ASSERT(cond)
	#endif

	#define MAXLINE 1024 // This sets the maximum line length in EAM input files.

	PairCDEAM::PairCDEAM(LAMMPS *lmp, int _cdeamVersion) : PairEAM(lmp), PairEAMAlloy(lmp), cdeamVersion(_cdeamVersion)
	{
	single_enable = 0;
	restartinfo = 0;

	rhoB = NULL;
	D_values = NULL;
	hcoeff = NULL;

	// Set communication buffer sizes needed by this pair style.
	if(cdeamVersion == 1) {
	comm_forward = 4;
	comm_reverse = 3;
	}
	else if(cdeamVersion == 2) {
	comm_forward = 3;
	comm_reverse = 2;
	}
	else {
	error->all(FLERR,"Invalid CD-EAM potential version.");
	}
	}

	PairCDEAM::~PairCDEAM()
	{
	memory->destroy(rhoB);
	memory->destroy(D_values);
	if(hcoeff) delete[] hcoeff;
	}

	void PairCDEAM::compute(int eflag, int vflag)
	{
	int i,j,ii,jj,inum,jnum,itype,jtype;
	double xtmp,ytmp,ztmp,delx,dely,delz,evdwl,fpair;
	double rsq,rhoip,rhojp,recip,phi;
	int ilist,jlist,numneigh,*firstneigh;

	evdwl = 0.0;
	if (eflag \|\| vflag) ev_setup(eflag,vflag);
	else evflag = vflag_fdotr = eflag_global = eflag_atom = 0;

	// Grow per-atom arrays if necessary
	if(atom->nmax > nmax) {
	memory->destroy(rho);
	memory->destroy(fp);
	memory->destroy(rhoB);
	memory->destroy(D_values);
	nmax = atom->nmax;
	memory->create(rho,nmax,"pair:rho");
	memory->create(rhoB,nmax,"pair:rhoB");
	memory->create(fp,nmax,"pair:fp");
	memory->create(D_values,nmax,"pair:D_values");
	}

	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;

	// Zero out per-atom arrays.
	int m = nlocal + atom->nghost;
	for(i = 0; i < m; i++) {
	rho[i] = 0.0;
	rhoB[i] = 0.0;
	D_values[i] = 0.0;
	}

	// Stage I

	// Compute rho and rhoB at each local atom site.
	// Additionally calculate the D_i values here if we are using the one-site formulation.
	// For the two-site formulation we have to calculate the D values in an extra loop (Stage II).
	for(ii = 0; ii < inum; ii++) {
	i = ilist[ii];
	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];
	j &= NEIGHMASK;

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

	if(rsq < cutforcesq) {
	jtype = type[j];
	double r = sqrt(rsq);
	const EAMTableIndex index = radiusToTableIndex(r);
	double localrho = RhoOfR(index, jtype, itype);
	rho[i] += localrho;
	if(jtype == speciesB) rhoB[i] += localrho;
	if(newton_pair \|\| j < nlocal) {
	localrho = RhoOfR(index, itype, jtype);
	rho[j] += localrho;
	if(itype == speciesB) rhoB[j] += localrho;
	}

	if(cdeamVersion == 1 && itype != jtype) {
	// Note: if the i-j interaction is not concentration dependent (because either
	// i or j are not species A or B) then its contribution to D_i and D_j should
	// be ignored.
	// This if-clause is only required for a ternary.
	if((itype == speciesA && jtype == speciesB) \|\| (jtype == speciesA && itype == speciesB)) {
	double Phi_AB = PhiOfR(index, itype, jtype, 1.0 / r);
	D_values[i] += Phi_AB;
	if(newton_pair \|\| j < nlocal)
	D_values[j] += Phi_AB;
	}
	}
	}
	}
	}

	// Communicate and sum densities.
	if(newton_pair) {
	communicationStage = 1;
	comm->reverse_comm_pair(this);
	}

	// fp = derivative of embedding energy at each atom
	// phi = embedding energy at each atom
	for(ii = 0; ii < inum; ii++) {
	i = ilist[ii];
	EAMTableIndex index = rhoToTableIndex(rho[i]);
	fp[i] = FPrimeOfRho(index, type[i]);
	if(eflag) {
	phi = FofRho(index, type[i]);
	if (eflag_global) eng_vdwl += phi;
	if (eflag_atom) eatom[i] += phi;
	}
	}

	// Communicate derivative of embedding function and densities
	// and D_values (this for one-site formulation only).
	communicationStage = 2;
	comm->forward_comm_pair(this);

	// The electron densities may not drop to zero because then the concentration would no longer be defined.
	// But the concentration is not needed anyway if there is no interaction with another atom, which is the case
	// if the electron density is exactly zero. That's why the following lines have been commented out.
	//
	//for(i = 0; i < nlocal + atom->nghost; i++) {
	// if(rho[i] == 0 && (type[i] == speciesA \|\| type[i] == speciesB))
	// error->one(FLERR,"CD-EAM potential routine: Detected atom with zero electron density.");
	//}

	// Stage II
	// This is only required for the original two-site formulation of the CD-EAM potential.

	if(cdeamVersion == 2) {
	// Compute intermediate value D_i for each atom.
	for(ii = 0; ii < inum; ii++) {
	i = ilist[ii];
	xtmp = x[i][0];
	ytmp = x[i][1];
	ztmp = x[i][2];
	itype = type[i];
	jlist = firstneigh[i];
	jnum = numneigh[i];

	// This code line is required for ternary alloys.
	if(itype != speciesA && itype != speciesB) continue;

	double x_i = rhoB[i] / rho[i]; // Concentration at atom i.

	for(jj = 0; jj < jnum; jj++) {
	j = jlist[jj];
	j &= NEIGHMASK;
	jtype = type[j];
	if(itype == jtype) continue;

	// This code line is required for ternary alloys.
	if(jtype != speciesA && jtype != speciesB) continue;

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

	if(rsq < cutforcesq) {
	double r = sqrt(rsq);
	const EAMTableIndex index = radiusToTableIndex(r);

	// The concentration independent part of the cross pair potential.
	double Phi_AB = PhiOfR(index, itype, jtype, 1.0 / r);

	// Average concentration of two sites
	double x_ij = 0.5 * (x_i + rhoB[j]/rho[j]);

	// Calculate derivative of h(x_ij) polynomial function.
	double h_prime = evalHprime(x_ij);

	D_values[i] += h_prime * Phi_AB / (2.0 * rho[i] * rho[i]);
	if(newton_pair \|\| j < nlocal)
	D_values[j] += h_prime * Phi_AB / (2.0 * rho[j] * rho[j]);
	}
	}
	}

	// Communicate and sum D values.
	if(newton_pair) {
	communicationStage = 3;
	comm->reverse_comm_pair(this);
	}
	communicationStage = 4;
	comm->forward_comm_pair(this);
	}

	// Stage III

	// Compute force acting on each atom.
	for(ii = 0; ii < inum; ii++) {
	i = ilist[ii];
	xtmp = x[i][0];
	ytmp = x[i][1];
	ztmp = x[i][2];
	itype = type[i];

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

	// Concentration at site i
	double x_i = -1.0; // The value -1 indicates: no concentration dependence for all interactions of atom i.
	// It will be replaced by the concentration at site i if atom i is either A or B.

	double D_i, h_prime_i;

	// This if-clause is only required for ternary alloys.
	if((itype == speciesA \|\| itype == speciesB) && rho[i] != 0.0) {

	// Compute local concentration at site i.
	x_i = rhoB[i]/rho[i];
	ASSERT(x_i >= 0 && x_i<=1.0);

	if(cdeamVersion == 1) {
	// Calculate derivative of h(x_i) polynomial function.
	h_prime_i = evalHprime(x_i);
	D_i = D_values[i] * h_prime_i / (2.0 * rho[i] * rho[i]);
	}
	else if(cdeamVersion == 2) {
	D_i = D_values[i];
	}
	else ASSERT(false);
	}

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

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

	if(rsq < cutforcesq) {
	jtype = type[j];
	double r = sqrt(rsq);
	const EAMTableIndex index = radiusToTableIndex(r);

	// rhoip = derivative of (density at atom j due to atom i)
	// rhojp = derivative of (density at atom i due to atom j)
	// psip needs both fp[i] and fp[j] terms since r_ij appears in two
	// terms of embed eng: Fi(sum rho_ij) and Fj(sum rho_ji)
	// hence embed' = Fi(sum rho_ij) rhojp + Fj(sum rho_ji) rhoip
	rhoip = RhoPrimeOfR(index, itype, jtype);
	rhojp = RhoPrimeOfR(index, jtype, itype);
	fpair = fp[i]rhojp + fp[j]rhoip;
	recip = 1.0/r;

	double x_j = -1; // The value -1 indicates: no concentration dependence for this i-j pair
	// because atom j is not of species A nor B.

	// This code line is required for ternary alloy.
	if(jtype == speciesA \|\| jtype == speciesB) {
	ASSERT(rho[i] != 0.0);
	ASSERT(rho[j] != 0.0);

	// Compute local concentration at site j.
	x_j = rhoB[j]/rho[j];
	ASSERT(x_j >= 0 && x_j<=1.0);

	double D_j;
	if(cdeamVersion == 1) {
	// Calculate derivative of h(x_j) polynomial function.
	double h_prime_j = evalHprime(x_j);
	D_j = D_values[j] * h_prime_j / (2.0 * rho[j] * rho[j]);
	}
	else if(cdeamVersion == 2) {
	D_j = D_values[j];
	}
	else ASSERT(false);

	double t2 = -rhoB[j];
	if(itype == speciesB) t2 += rho[j];
	fpair += D_j * rhoip * t2;
	}

	// This if-clause is only required for a ternary alloy.
	// Actually we don't need it at all because D_i should be zero anyway if
	// atom i has no concentration dependent interactions (because it is not species A or B).
	if(x_i != -1.0) {
	double t1 = -rhoB[i];
	if(jtype == speciesB) t1 += rho[i];
	fpair += D_i * rhojp * t1;
	}

	double phip;
	double phi = PhiOfR(index, itype, jtype, recip, phip);
	if(itype == jtype \|\| x_i == -1.0 \|\| x_j == -1.0) {
	// Case of no concentration dependence.
	fpair += phip;
	}
	else {
	// We have a concentration dependence for the i-j interaction.
	double h;
	if(cdeamVersion == 1) {
	// Calculate h(x_i) polynomial function.
	double h_i = evalH(x_i);
	// Calculate h(x_j) polynomial function.
	double h_j = evalH(x_j);
	h = 0.5 * (h_i + h_j);
	}
	else if(cdeamVersion == 2) {
	// Average concentration.
	double x_ij = 0.5 * (x_i + x_j);
	// Calculate h(x_ij) polynomial function.
	h = evalH(x_ij);
	}
	else ASSERT(false);
	fpair += h * phip;
	phi *= h;
	}

	// Divide by r_ij and negate to get forces from gradient.
	fpair /= -r;

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

	if(vflag_fdotr) virial_fdotr_compute();
	}

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

	void PairCDEAM::coeff(int narg, char **arg)
	{
	PairEAMAlloy::coeff(narg, arg);

	// Make sure the EAM file is a CD-EAM binary alloy.
	if(setfl->nelements < 2)
	error->all(FLERR,"The EAM file must contain at least 2 elements to be used with the eam/cd pair style.");

	// Read in the coefficients of the h polynomial from the end of the EAM file.
	read_h_coeff(arg[2]);

	// Determine which atom type is the A species and which is the B species in the alloy.
	// By default take the first element (index 0) in the EAM file as the A species
	// and the second element (index 1) in the EAM file as the B species.
	speciesA = -1;
	speciesB = -1;
	for(int i = 1; i <= atom->ntypes; i++) {
	if(map[i] == 0) {
	if(speciesA >= 0)
	error->all(FLERR,"The first element from the EAM file may only be mapped to a single atom type.");
	speciesA = i;
	}
	if(map[i] == 1) {
	if(speciesB >= 0)
	error->all(FLERR,"The second element from the EAM file may only be mapped to a single atom type.");
	speciesB = i;
	}
	}
	if(speciesA < 0)
	error->all(FLERR,"The first element from the EAM file must be mapped to exactly one atom type.");
	if(speciesB < 0)
	error->all(FLERR,"The second element from the EAM file must be mapped to exactly one atom type.");
	}

	/* ----------------------------------------------------------------------
	Reads in the h(x) polynomial coefficients
	------------------------------------------------------------------------- */
	void PairCDEAM::read_h_coeff(char *filename)
	{
	if(comm->me == 0) {
	// Open potential file
	FILE *fp;
	char line[MAXLINE];
	char nextline[MAXLINE];
	fp = fopen(filename,"r");
	if (fp == NULL) {
	char str[128];
	sprintf(str,"Cannot open EAM potential file %s", filename);
	error->one(FLERR,str);
	}

	// h coefficients are stored at the end of the file.
	// Skip to last line of file.
	while(fgets(nextline, MAXLINE, fp) != NULL) {
	strcpy(line, nextline);
	}
	char* ptr = strtok(line, " \t\n\r\f");
	int degree = atoi(ptr);
	nhcoeff = degree+1;
	hcoeff = new double[nhcoeff];
	int i = 0;
	while((ptr = strtok(NULL," \t\n\r\f")) != NULL && i < nhcoeff) {
	hcoeff[i++] = atof(ptr);
	}
	if(i != nhcoeff \|\| nhcoeff < 1)
	error->one(FLERR,"Failed to read h(x) function coefficients from EAM file.");

	// Close the potential file.
	fclose(fp);
	}

	MPI_Bcast(&nhcoeff, 1, MPI_INT, 0, world);
	if(comm->me != 0) hcoeff = new double[nhcoeff];
	MPI_Bcast(hcoeff, nhcoeff, MPI_DOUBLE, 0, world);
	}


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

	int PairCDEAM::pack_comm(int n, int list, double buf, int pbc_flag, int *pbc)
	{
	int i,j,m;

	m = 0;
	if(communicationStage == 2) {
	if(cdeamVersion == 1) {
	for (i = 0; i < n; i++) {
	j = list[i];
	buf[m++] = fp[j];
	buf[m++] = rho[j];
	buf[m++] = rhoB[j];
	buf[m++] = D_values[j];
	}
	return 4;
	}
	else if(cdeamVersion == 2) {
	for (i = 0; i < n; i++) {
	j = list[i];
	buf[m++] = fp[j];
	buf[m++] = rho[j];
	buf[m++] = rhoB[j];
	}
	return 3;
	}
	else { ASSERT(false); return 0; }
	}
	else if(communicationStage == 4) {
	for (i = 0; i < n; i++) {
	j = list[i];
	buf[m++] = D_values[j];
	}
	return 1;
	}
	else return 0;
	}

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

	void PairCDEAM::unpack_comm(int n, int first, double *buf)
	{
	int i,m,last;

	m = 0;
	last = first + n;
	if(communicationStage == 2) {
	if(cdeamVersion == 1) {
	for(i = first; i < last; i++) {
	fp[i] = buf[m++];
	rho[i] = buf[m++];
	rhoB[i] = buf[m++];
	D_values[i] = buf[m++];
	}
	}
	else if(cdeamVersion == 2) {
	for(i = first; i < last; i++) {
	fp[i] = buf[m++];
	rho[i] = buf[m++];
	rhoB[i] = buf[m++];
	}
	}
	else ASSERT(false);
	}
	else if(communicationStage == 4) {
	for(i = first; i < last; i++) {
	D_values[i] = buf[m++];
	}
	}
	}

	/* ---------------------------------------------------------------------- */
	int PairCDEAM::pack_reverse_comm(int n, int first, double *buf)
	{
	int i,m,last;

	m = 0;
	last = first + n;

	if(communicationStage == 1) {
	if(cdeamVersion == 1) {
	for(i = first; i < last; i++) {
	buf[m++] = rho[i];
	buf[m++] = rhoB[i];
	buf[m++] = D_values[i];
	}
	return 3;
	}
	else if(cdeamVersion == 2) {
	for(i = first; i < last; i++) {
	buf[m++] = rho[i];
	buf[m++] = rhoB[i];
	}
	return 2;
	}
	else { ASSERT(false); return 0; }
	}
	else if(communicationStage == 3) {
	for(i = first; i < last; i++) {
	buf[m++] = D_values[i];
	}
	return 1;
	}
	else return 0;
	}

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

	void PairCDEAM::unpack_reverse_comm(int n, int list, double buf)
	{
	int i,j,m;

	m = 0;
	if(communicationStage == 1) {
	if(cdeamVersion == 1) {
	for(i = 0; i < n; i++) {
	j = list[i];
	rho[j] += buf[m++];
	rhoB[j] += buf[m++];
	D_values[j] += buf[m++];
	}
	}
	else if(cdeamVersion == 2) {
	for(i = 0; i < n; i++) {
	j = list[i];
	rho[j] += buf[m++];
	rhoB[j] += buf[m++];
	}
	}
	else ASSERT(false);
	}
	else if(communicationStage == 3) {
	for(i = 0; i < n; i++) {
	j = list[i];
	D_values[j] += buf[m++];
	}
	}
	}

	/* ----------------------------------------------------------------------
	memory usage of local atom-based arrays
	------------------------------------------------------------------------- */
	double PairCDEAM::memory_usage()
	{
	double bytes = 2 * nmax * sizeof(double);
	return PairEAMAlloy::memory_usage() + bytes;
	}

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