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angle_cosine_shift_exp.cpp
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Wed, Feb 19, 00:06

angle_cosine_shift_exp.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: Carsten Svaneborg, science@zqex.dk
------------------------------------------------------------------------- */
#include <math.h>
#include <stdlib.h>
#include "angle_cosine_shift_exp.h"
#include "atom.h"
#include "neighbor.h"
#include "domain.h"
#include "comm.h"
#include "force.h"
#include "math_const.h"
#include "memory.h"
#include "error.h"
using namespace LAMMPS_NS;
using namespace MathConst;
#define SMALL 0.001
/* ---------------------------------------------------------------------- */
AngleCosineShiftExp::AngleCosineShiftExp(LAMMPS *lmp) : Angle(lmp) {}
/* ---------------------------------------------------------------------- */
AngleCosineShiftExp::~AngleCosineShiftExp()
{
if (allocated) {
memory->destroy(setflag);
memory->destroy(umin);
memory->destroy(a);
memory->destroy(opt1);
memory->destroy(cost);
memory->destroy(sint);
memory->destroy(theta0);
memory->destroy(doExpansion);
}
}
/* ---------------------------------------------------------------------- */
void AngleCosineShiftExp::compute(int eflag, int vflag)
{
int i1,i2,i3,n,type;
double delx1,dely1,delz1,delx2,dely2,delz2;
double eangle,f1[3],f3[3],ff;
double rsq1,rsq2,r1,r2,c,s,a11,a12,a22;
double exp2,aa,uumin,cccpsss,cssmscc;
eangle = 0.0;
if (eflag || vflag) ev_setup(eflag,vflag);
else evflag = 0;
double **x = atom->x;
double **f = atom->f;
int **anglelist = neighbor->anglelist;
int nanglelist = neighbor->nanglelist;
int nlocal = atom->nlocal;
int newton_bond = force->newton_bond;
for (n = 0; n < nanglelist; n++) {
i1 = anglelist[n][0];
i2 = anglelist[n][1];
i3 = anglelist[n][2];
type = anglelist[n][3];
// 1st bond
delx1 = x[i1][0] - x[i2][0];
dely1 = x[i1][1] - x[i2][1];
delz1 = x[i1][2] - x[i2][2];
rsq1 = delx1*delx1 + dely1*dely1 + delz1*delz1;
r1 = sqrt(rsq1);
// 2nd bond
delx2 = x[i3][0] - x[i2][0];
dely2 = x[i3][1] - x[i2][1];
delz2 = x[i3][2] - x[i2][2];
rsq2 = delx2*delx2 + dely2*dely2 + delz2*delz2;
r2 = sqrt(rsq2);
// c = cosine of angle
c = delx1*delx2 + dely1*dely2 + delz1*delz2;
c /= r1*r2;
if (c > 1.0) c = 1.0;
if (c < -1.0) c = -1.0;
// C= sine of angle
s = sqrt(1.0 - c*c);
if (s < SMALL) s = SMALL;
// force & energy
aa=a[type];
uumin=umin[type];
cccpsss = c*cost[type]+s*sint[type];
cssmscc = c*sint[type]-s*cost[type];
if (doExpansion[type])
{ // |a|<0.01 so use expansions relative precision <1e-5
// std::cout << "Using expansion\n";
if (eflag) eangle = -0.125*(1+cccpsss)*(4+aa*(cccpsss-1))*uumin;
ff=0.25*uumin*cssmscc*(2+aa*cccpsss)/s;
}
else
{
// std::cout << "Not using expansion\n";
exp2=exp(0.5*aa*(1+cccpsss));
if (eflag) eangle = opt1[type]*(1-exp2);
ff=0.5*a[type]*opt1[type]*exp2*cssmscc/s;
}
a11 = ff*c/ rsq1;
a12 = -ff / (r1*r2);
a22 = ff*c/ rsq2;
f1[0] = a11*delx1 + a12*delx2;
f1[1] = a11*dely1 + a12*dely2;
f1[2] = a11*delz1 + a12*delz2;
f3[0] = a22*delx2 + a12*delx1;
f3[1] = a22*dely2 + a12*dely1;
f3[2] = a22*delz2 + a12*delz1;
// apply force to each of 3 atoms
if (newton_bond || i1 < nlocal) {
f[i1][0] += f1[0];
f[i1][1] += f1[1];
f[i1][2] += f1[2];
}
if (newton_bond || i2 < nlocal) {
f[i2][0] -= f1[0] + f3[0];
f[i2][1] -= f1[1] + f3[1];
f[i2][2] -= f1[2] + f3[2];
}
if (newton_bond || i3 < nlocal) {
f[i3][0] += f3[0];
f[i3][1] += f3[1];
f[i3][2] += f3[2];
}
if (evflag) ev_tally(i1,i2,i3,nlocal,newton_bond,eangle,f1,f3,
delx1,dely1,delz1,delx2,dely2,delz2);
}
}
/* ---------------------------------------------------------------------- */
void AngleCosineShiftExp::allocate()
{
allocated = 1;
int n = atom->nangletypes;
memory->create(doExpansion, n+1, "angle:doExpansion");
memory->create(umin , n+1, "angle:umin");
memory->create(a , n+1, "angle:a");
memory->create(sint , n+1, "angle:sint");
memory->create(cost , n+1, "angle:cost");
memory->create(opt1 , n+1, "angle:opt1");
memory->create(theta0 , n+1, "angle:theta0");
memory->create(setflag , n+1, "angle:setflag");
for (int i = 1; i <= n; i++) setflag[i] = 0;
}
/* ----------------------------------------------------------------------
set coeffs for one type
------------------------------------------------------------------------- */
void AngleCosineShiftExp::coeff(int narg, char **arg)
{
if (narg != 4) error->all(FLERR,"Incorrect args for angle coefficients");
if (!allocated) allocate();
int ilo,ihi;
force->bounds(arg[0],atom->nangletypes,ilo,ihi);
double umin_ = force->numeric(FLERR,arg[1]);
double theta0_ = force->numeric(FLERR,arg[2]);
double a_ = force->numeric(FLERR,arg[3]);
int count = 0;
for (int i = ilo; i <= ihi; i++) {
doExpansion[i]=(fabs(a_)<0.001);
umin[i] = umin_;
a[i] = a_;
cost[i] = cos(theta0_*MY_PI / 180.0);
sint[i] = sin(theta0_*MY_PI / 180.0);
theta0[i]= theta0_*MY_PI / 180.0;
if (!doExpansion[i]) opt1[i]=umin_/(exp(a_)-1);
setflag[i] = 1;
count++;
}
if (count == 0) error->all(FLERR,"Incorrect args for angle coefficients");
}
/* ---------------------------------------------------------------------- */
double AngleCosineShiftExp::equilibrium_angle(int i)
{
return theta0[i];
}
/* ----------------------------------------------------------------------
proc 0 writes out coeffs to restart file
------------------------------------------------------------------------- */
void AngleCosineShiftExp::write_restart(FILE *fp)
{
fwrite(&umin[1],sizeof(double),atom->nangletypes,fp);
fwrite(&a[1],sizeof(double),atom->nangletypes,fp);
fwrite(&cost[1],sizeof(double),atom->nangletypes,fp);
fwrite(&sint[1],sizeof(double),atom->nangletypes,fp);
fwrite(&theta0[1],sizeof(double),atom->nangletypes,fp);
}
/* ----------------------------------------------------------------------
proc 0 reads coeffs from restart file, bcasts them
------------------------------------------------------------------------- */
void AngleCosineShiftExp::read_restart(FILE *fp)
{
allocate();
if (comm->me == 0)
{
fread(&umin[1],sizeof(double),atom->nangletypes,fp);
fread(&a[1],sizeof(double),atom->nangletypes,fp);
fread(&cost[1],sizeof(double),atom->nangletypes,fp);
fread(&sint[1],sizeof(double),atom->nangletypes,fp);
fread(&theta0[1],sizeof(double),atom->nangletypes,fp);
}
MPI_Bcast(&umin[1],atom->nangletypes,MPI_DOUBLE,0,world);
MPI_Bcast(&a[1],atom->nangletypes,MPI_DOUBLE,0,world);
MPI_Bcast(&cost[1],atom->nangletypes,MPI_DOUBLE,0,world);
MPI_Bcast(&sint[1],atom->nangletypes,MPI_DOUBLE,0,world);
MPI_Bcast(&theta0[1],atom->nangletypes,MPI_DOUBLE,0,world);
for (int i = 1; i <= atom->nangletypes; i++)
{
setflag[i] = 1;
doExpansion[i]=(fabs(a[i])<0.01);
if (!doExpansion[i]) opt1[i]=umin[i]/(exp(a[i])-1);
}
}
/* ----------------------------------------------------------------------
proc 0 writes to data file
------------------------------------------------------------------------- */
void AngleCosineShiftExp::write_data(FILE *fp)
{
for (int i = 1; i <= atom->nangletypes; i++)
fprintf(fp,"%d %g %g %g\n",i,umin[i],theta0[i]/MY_PI*180.0,a[i]);
}
/* ---------------------------------------------------------------------- */
double AngleCosineShiftExp::single(int type, int i1, int i2, int i3)
{
double **x = atom->x;
double delx1 = x[i1][0] - x[i2][0];
double dely1 = x[i1][1] - x[i2][1];
double delz1 = x[i1][2] - x[i2][2];
domain->minimum_image(delx1,dely1,delz1);
double r1 = sqrt(delx1*delx1 + dely1*dely1 + delz1*delz1);
double delx2 = x[i3][0] - x[i2][0];
double dely2 = x[i3][1] - x[i2][1];
double delz2 = x[i3][2] - x[i2][2];
domain->minimum_image(delx2,dely2,delz2);
double r2 = sqrt(delx2*delx2 + dely2*dely2 + delz2*delz2);
double c = delx1*delx2 + dely1*dely2 + delz1*delz2;
c /= r1*r2;
if (c > 1.0) c = 1.0;
if (c < -1.0) c = -1.0;
double s=sqrt(1.0-c*c);
double cccpsss=c*cost[type]+s*sint[type];
if (doExpansion[type])
{
return -0.125*(1+cccpsss)*(4+a[type]*(cccpsss-1))*umin[type];
}
else
{
return opt1[type]*(1-exp(0.5*a[type]*(1+cccpsss)));
}
}

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