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improper_harmonic.cpp
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Sun, Jun 2, 22:20

improper_harmonic.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.
------------------------------------------------------------------------- */
#include "lmptype.h"
#include "mpi.h"
#include "math.h"
#include "stdlib.h"
#include "improper_harmonic.h"
#include "atom.h"
#include "comm.h"
#include "neighbor.h"
#include "domain.h"
#include "force.h"
#include "update.h"
#include "math_const.h"
#include "memory.h"
#include "error.h"
using namespace LAMMPS_NS;
using namespace MathConst;
#define TOLERANCE 0.05
#define SMALL 0.001
/* ---------------------------------------------------------------------- */
ImproperHarmonic::ImproperHarmonic(LAMMPS *lmp) : Improper(lmp)
{
writedata = 1;
}
/* ---------------------------------------------------------------------- */
ImproperHarmonic::~ImproperHarmonic()
{
if (allocated) {
memory->destroy(setflag);
memory->destroy(k);
memory->destroy(chi);
}
}
/* ---------------------------------------------------------------------- */
void ImproperHarmonic::compute(int eflag, int vflag)
{
int i1,i2,i3,i4,n,type;
double vb1x,vb1y,vb1z,vb2x,vb2y,vb2z,vb3x,vb3y,vb3z;
double eimproper,f1[3],f2[3],f3[3],f4[3];
double ss1,ss2,ss3,r1,r2,r3,c0,c1,c2,s1,s2;
double s12,c,s,domega,a,a11,a22,a33,a12,a13,a23;
double sx2,sy2,sz2;
eimproper = 0.0;
if (eflag || vflag) ev_setup(eflag,vflag);
else evflag = 0;
double **x = atom->x;
double **f = atom->f;
int **improperlist = neighbor->improperlist;
int nimproperlist = neighbor->nimproperlist;
int nlocal = atom->nlocal;
int newton_bond = force->newton_bond;
for (n = 0; n < nimproperlist; n++) {
i1 = improperlist[n][0];
i2 = improperlist[n][1];
i3 = improperlist[n][2];
i4 = improperlist[n][3];
type = improperlist[n][4];
// geometry of 4-body
vb1x = x[i1][0] - x[i2][0];
vb1y = x[i1][1] - x[i2][1];
vb1z = x[i1][2] - x[i2][2];
vb2x = x[i3][0] - x[i2][0];
vb2y = x[i3][1] - x[i2][1];
vb2z = x[i3][2] - x[i2][2];
vb3x = x[i4][0] - x[i3][0];
vb3y = x[i4][1] - x[i3][1];
vb3z = x[i4][2] - x[i3][2];
ss1 = 1.0 / (vb1x*vb1x + vb1y*vb1y + vb1z*vb1z);
ss2 = 1.0 / (vb2x*vb2x + vb2y*vb2y + vb2z*vb2z);
ss3 = 1.0 / (vb3x*vb3x + vb3y*vb3y + vb3z*vb3z);
r1 = sqrt(ss1);
r2 = sqrt(ss2);
r3 = sqrt(ss3);
// sin and cos of angle
c0 = (vb1x * vb3x + vb1y * vb3y + vb1z * vb3z) * r1 * r3;
c1 = (vb1x * vb2x + vb1y * vb2y + vb1z * vb2z) * r1 * r2;
c2 = -(vb3x * vb2x + vb3y * vb2y + vb3z * vb2z) * r3 * r2;
s1 = 1.0 - c1*c1;
if (s1 < SMALL) s1 = SMALL;
s1 = 1.0 / s1;
s2 = 1.0 - c2*c2;
if (s2 < SMALL) s2 = SMALL;
s2 = 1.0 / s2;
s12 = sqrt(s1*s2);
c = (c1*c2 + c0) * s12;
// error check
if (c > 1.0 + TOLERANCE || c < (-1.0 - TOLERANCE)) {
int me;
MPI_Comm_rank(world,&me);
if (screen) {
char str[128];
sprintf(str,"Improper problem: %d " BIGINT_FORMAT " "
TAGINT_FORMAT " " TAGINT_FORMAT " "
TAGINT_FORMAT " " TAGINT_FORMAT,
me,update->ntimestep,
atom->tag[i1],atom->tag[i2],atom->tag[i3],atom->tag[i4]);
error->warning(FLERR,str,0);
fprintf(screen," 1st atom: %d %g %g %g\n",
me,x[i1][0],x[i1][1],x[i1][2]);
fprintf(screen," 2nd atom: %d %g %g %g\n",
me,x[i2][0],x[i2][1],x[i2][2]);
fprintf(screen," 3rd atom: %d %g %g %g\n",
me,x[i3][0],x[i3][1],x[i3][2]);
fprintf(screen," 4th atom: %d %g %g %g\n",
me,x[i4][0],x[i4][1],x[i4][2]);
}
}
if (c > 1.0) c = 1.0;
if (c < -1.0) c = -1.0;
s = sqrt(1.0 - c*c);
if (s < SMALL) s = SMALL;
// force & energy
domega = acos(c) - chi[type];
a = k[type] * domega;
if (eflag) eimproper = a*domega;
a = -a * 2.0/s;
c = c * a;
s12 = s12 * a;
a11 = c*ss1*s1;
a22 = -ss2 * (2.0*c0*s12 - c*(s1+s2));
a33 = c*ss3*s2;
a12 = -r1*r2*(c1*c*s1 + c2*s12);
a13 = -r1*r3*s12;
a23 = r2*r3*(c2*c*s2 + c1*s12);
sx2 = a22*vb2x + a23*vb3x + a12*vb1x;
sy2 = a22*vb2y + a23*vb3y + a12*vb1y;
sz2 = a22*vb2z + a23*vb3z + a12*vb1z;
f1[0] = a12*vb2x + a13*vb3x + a11*vb1x;
f1[1] = a12*vb2y + a13*vb3y + a11*vb1y;
f1[2] = a12*vb2z + a13*vb3z + a11*vb1z;
f2[0] = -sx2 - f1[0];
f2[1] = -sy2 - f1[1];
f2[2] = -sz2 - f1[2];
f4[0] = a23*vb2x + a33*vb3x + a13*vb1x;
f4[1] = a23*vb2y + a33*vb3y + a13*vb1y;
f4[2] = a23*vb2z + a33*vb3z + a13*vb1z;
f3[0] = sx2 - f4[0];
f3[1] = sy2 - f4[1];
f3[2] = sz2 - f4[2];
// apply force to each of 4 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] += f2[0];
f[i2][1] += f2[1];
f[i2][2] += f2[2];
}
if (newton_bond || i3 < nlocal) {
f[i3][0] += f3[0];
f[i3][1] += f3[1];
f[i3][2] += f3[2];
}
if (newton_bond || i4 < nlocal) {
f[i4][0] += f4[0];
f[i4][1] += f4[1];
f[i4][2] += f4[2];
}
if (evflag)
ev_tally(i1,i2,i3,i4,nlocal,newton_bond,eimproper,f1,f3,f4,
vb1x,vb1y,vb1z,vb2x,vb2y,vb2z,vb3x,vb3y,vb3z);
}
}
/* ---------------------------------------------------------------------- */
void ImproperHarmonic::allocate()
{
allocated = 1;
int n = atom->nimpropertypes;
memory->create(k,n+1,"improper:k");
memory->create(chi,n+1,"improper:chi");
memory->create(setflag,n+1,"improper:setflag");
for (int i = 1; i <= n; i++) setflag[i] = 0;
}
/* ----------------------------------------------------------------------
set coeffs for one type
------------------------------------------------------------------------- */
void ImproperHarmonic::coeff(int narg, char **arg)
{
if (narg != 3) error->all(FLERR,"Incorrect args for improper coefficients");
if (!allocated) allocate();
int ilo,ihi;
force->bounds(arg[0],atom->nimpropertypes,ilo,ihi);
double k_one = force->numeric(FLERR,arg[1]);
double chi_one = force->numeric(FLERR,arg[2]);
// convert chi from degrees to radians
int count = 0;
for (int i = ilo; i <= ihi; i++) {
k[i] = k_one;
chi[i] = chi_one/180.0 * MY_PI;
setflag[i] = 1;
count++;
}
if (count == 0) error->all(FLERR,"Incorrect args for improper coefficients");
}
/* ----------------------------------------------------------------------
proc 0 writes out coeffs to restart file
------------------------------------------------------------------------- */
void ImproperHarmonic::write_restart(FILE *fp)
{
fwrite(&k[1],sizeof(double),atom->nimpropertypes,fp);
fwrite(&chi[1],sizeof(double),atom->nimpropertypes,fp);
}
/* ----------------------------------------------------------------------
proc 0 reads coeffs from restart file, bcasts them
------------------------------------------------------------------------- */
void ImproperHarmonic::read_restart(FILE *fp)
{
allocate();
if (comm->me == 0) {
fread(&k[1],sizeof(double),atom->nimpropertypes,fp);
fread(&chi[1],sizeof(double),atom->nimpropertypes,fp);
}
MPI_Bcast(&k[1],atom->nimpropertypes,MPI_DOUBLE,0,world);
MPI_Bcast(&chi[1],atom->nimpropertypes,MPI_DOUBLE,0,world);
for (int i = 1; i <= atom->nimpropertypes; i++) setflag[i] = 1;
}
/* ----------------------------------------------------------------------
proc 0 writes to data file
------------------------------------------------------------------------- */
void ImproperHarmonic::write_data(FILE *fp)
{
for (int i = 1; i <= atom->nimpropertypes; i++)
fprintf(fp,"%d %g %g\n",i,k[i],chi[i]/MY_PI*180.0);
}

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