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lammps/src/MOLECULE/angle_cosine_periodic.cpp
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angle_cosine_periodic.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: Tod A Pascal (Caltech)
------------------------------------------------------------------------- */
#include "math.h"
#include "stdlib.h"
#include "angle_cosine_periodic.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
/* ---------------------------------------------------------------------- */
AngleCosinePeriodic::AngleCosinePeriodic(LAMMPS *lmp) : Angle(lmp) {}
/* ---------------------------------------------------------------------- */
AngleCosinePeriodic::~AngleCosinePeriodic()
{
if (allocated) {
memory->destroy(setflag);
memory->destroy(k);
memory->destroy(b);
memory->destroy(multiplicity);
}
}
/* ---------------------------------------------------------------------- */
void AngleCosinePeriodic::compute(int eflag, int vflag)
{
int i,i1,i2,i3,n,m,type,b_factor;
double delx1,dely1,delz1,delx2,dely2,delz2;
double eangle,f1[3],f3[3];
double rsq1,rsq2,r1,r2,c,s,a,a11,a12,a22;
double tn,tn_1,tn_2,un,un_1,un_2;
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];
domain->minimum_image(delx1,dely1,delz1);
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];
domain->minimum_image(delx2,dely2,delz2);
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;
m = multiplicity[type];
b_factor = b[type];
// cos(n*x) = Tn(cos(x))
// Tn(x) = Chebyshev polynomials of the first kind: T_0 = 1, T_1 = x, ...
// recurrence relationship:
// Tn(x) = 2*x*T[n-1](x) - T[n-2](x) where T[-1](x) = 0
// also, dTn(x)/dx = n*U[n-1](x)
// where Un(x) = 2*x*U[n-1](x) - U[n-2](x) and U[-1](x) = 0
// finally need to handle special case for n = 1
tn = 1.0;
tn_1 = 1.0;
tn_2 = 0.0;
un = 1.0;
un_1 = 2.0;
un_2 = 0.0;
s = sqrt(1.0 - c*c);
if (s < SMALL) s = SMALL;
s = 1.0/s;
// force & energy
tn_2 = c;
for (i = 1; i <= m; i++) {
tn = 2*c*tn_1 - tn_2;
tn_2 = tn_1;
tn_1 = tn;
}
for (i = 2; i <= m; i++) {
un = 2*c*un_1 - un_2;
un_2 = un_1;
un_1 = un;
}
tn = b_factor*pow(-1.0,m)*tn;
un = b_factor*pow(-1.0,m)*m*un;
if (eflag) eangle = 2*k[type]*(1.0 - tn);
a = -k[type]*un;
a11 = a*c / rsq1;
a12 = -a / (r1*r2);
a22 = a*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 AngleCosinePeriodic::allocate()
{
allocated = 1;
int n = atom->nangletypes;
memory->create(k,n+1,"angle:k");
memory->create(multiplicity,n+1,"angle:multiplicity");
memory->create(b,n+1,"angle:b");
memory->create(setflag,n+1,"angle:setflag");
for (int i = 1; i <= n; i++) setflag[i] = 0;
}
/* ----------------------------------------------------------------------
set coeffs for one or more types
------------------------------------------------------------------------- */
void AngleCosinePeriodic::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 c_one = atof(arg[1]);
int b_one = atoi(arg[2]);
int n_one = atoi(arg[3]);
if (n_one <= 0) error->all(FLERR,"Incorrect args for angle coefficients");
int count = 0;
for (int i = ilo; i <= ihi; i++) {
k[i] = c_one/(n_one*n_one);
b[i] = b_one;
multiplicity[i] = n_one;
setflag[i] = 1;
count++;
}
if (count == 0) error->all(FLERR,"Incorrect args for angle coefficients");
}
/* ---------------------------------------------------------------------- */
double AngleCosinePeriodic::equilibrium_angle(int i)
{
return MY_PI;
}
/* ----------------------------------------------------------------------
proc 0 writes out coeffs to restart file
------------------------------------------------------------------------- */
void AngleCosinePeriodic::write_restart(FILE *fp)
{
fwrite(&k[1],sizeof(double),atom->nangletypes,fp);
fwrite(&b[1],sizeof(int),atom->nangletypes,fp);
fwrite(&multiplicity[1],sizeof(int),atom->nangletypes,fp);
}
/* ----------------------------------------------------------------------
proc 0 reads coeffs from restart file, bcasts them
------------------------------------------------------------------------- */
void AngleCosinePeriodic::read_restart(FILE *fp)
{
allocate();
if (comm->me == 0) {
fread(&k[1],sizeof(double),atom->nangletypes,fp);
fread(&b[1],sizeof(int),atom->nangletypes,fp);
fread(&multiplicity[1],sizeof(int),atom->nangletypes,fp);
}
MPI_Bcast(&k[1],atom->nangletypes,MPI_DOUBLE,0,world);
MPI_Bcast(&b[1],atom->nangletypes,MPI_INT,0,world);
MPI_Bcast(&multiplicity[1],atom->nangletypes,MPI_INT,0,world);
for (int i = 1; i <= atom->nangletypes; i++) setflag[i] = 1;
}
/* ---------------------------------------------------------------------- */
double AngleCosinePeriodic::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;
c = cos(acos(c)*multiplicity[type]);
return k[type]*(1.0-b[type]*pow(-1.0,multiplicity[type])*c);
}
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