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lammps/src/dihedral_opls.cpp
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dihedral_opls.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
www.cs.sandia.gov/~sjplimp/lammps.html
Steve Plimpton, sjplimp@sandia.gov, Sandia National Laboratories
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: Mark Stevens (SNL)
------------------------------------------------------------------------- */
#include "math.h"
#include "stdlib.h"
#include "dihedral_opls.h"
#include "atom.h"
#include "comm.h"
#include "neighbor.h"
#include "domain.h"
#include "force.h"
#include "update.h"
#include "memory.h"
#include "error.h"
#define MIN(A,B) ((A) < (B)) ? (A) : (B)
#define MAX(A,B) ((A) > (B)) ? (A) : (B)
#define TOLERANCE 0.05
#define SMALL 0.001
#define SMALLER 0.00001
/* ----------------------------------------------------------------------
free all arrays
------------------------------------------------------------------------- */
DihedralOPLS::~DihedralOPLS()
{
if (allocated) {
memory->sfree(setflag);
memory->sfree(k1);
memory->sfree(k2);
memory->sfree(k3);
memory->sfree(k4);
}
}
/* ---------------------------------------------------------------------- */
void DihedralOPLS::compute(int eflag, int vflag)
{
int i,m,n,i1,i2,i3,i4,type,factor;
double rfactor;
double vb1x,vb1y,vb1z,vb2x,vb2y;
double vb2z,vb2xm,vb2ym,vb2zm,vb3x,vb3y,vb3z,sb1;
double sb2,sb3,rb1,rb3,c0,b1mag2,b1mag,b2mag2;
double b2mag,b3mag2,b3mag,ctmp,r12c1,c1mag,r12c2;
double c2mag,sc1,sc2,s1,s12,c,p,pd,a,a11,a22;
double a33,a12,a13,a23,sx1,sx2,sx12,sy1,sy2,sy12;
double sz1,sz2,sz12,s2,cx,cy,cz,cmag,dx,phi,si,siinv,sin2;
energy = 0.0;
if (vflag) for (n = 0; n < 6; n++) virial[n] = 0.0;
double **x = atom->x;
double **f = atom->f;
int **dihedrallist = neighbor->dihedrallist;
int ndihedrallist = neighbor->ndihedrallist;
int nlocal = atom->nlocal;
int newton_bond = force->newton_bond;
for (n = 0; n < ndihedrallist; n++) {
i1 = dihedrallist[n][0];
i2 = dihedrallist[n][1];
i3 = dihedrallist[n][2];
i4 = dihedrallist[n][3];
type = dihedrallist[n][4];
if (newton_bond) factor = 4;
else {
factor = 0;
if (i1 < nlocal) factor++;
if (i2 < nlocal) factor++;
if (i3 < nlocal) factor++;
if (i4 < nlocal) factor++;
}
rfactor = 0.25 * factor;
// 1st bond
vb1x = x[i1][0] - x[i2][0];
vb1y = x[i1][1] - x[i2][1];
vb1z = x[i1][2] - x[i2][2];
domain->minimum_image(&vb1x,&vb1y,&vb1z);
// 2nd bond
vb2x = x[i3][0] - x[i2][0];
vb2y = x[i3][1] - x[i2][1];
vb2z = x[i3][2] - x[i2][2];
domain->minimum_image(&vb2x,&vb2y,&vb2z);
vb2xm = -vb2x;
vb2ym = -vb2y;
vb2zm = -vb2z;
domain->minimum_image(&vb2xm,&vb2ym,&vb2zm);
// 3rd bond
vb3x = x[i4][0] - x[i3][0];
vb3y = x[i4][1] - x[i3][1];
vb3z = x[i4][2] - x[i3][2];
domain->minimum_image(&vb3x,&vb3y,&vb3z);
// c0 calculation
sb1 = 1.0 / (vb1x*vb1x + vb1y*vb1y + vb1z*vb1z);
sb2 = 1.0 / (vb2x*vb2x + vb2y*vb2y + vb2z*vb2z);
sb3 = 1.0 / (vb3x*vb3x + vb3y*vb3y + vb3z*vb3z);
rb1 = sqrt(sb1);
rb3 = sqrt(sb3);
c0 = (vb1x*vb3x + vb1y*vb3y + vb1z*vb3z) * rb1*rb3;
// 1st and 2nd angle
b1mag2 = vb1x*vb1x + vb1y*vb1y + vb1z*vb1z;
b1mag = sqrt(b1mag2);
b2mag2 = vb2x*vb2x + vb2y*vb2y + vb2z*vb2z;
b2mag = sqrt(b2mag2);
b3mag2 = vb3x*vb3x + vb3y*vb3y + vb3z*vb3z;
b3mag = sqrt(b3mag2);
ctmp = vb1x*vb2x + vb1y*vb2y + vb1z*vb2z;
r12c1 = 1.0 / (b1mag*b2mag);
c1mag = ctmp * r12c1;
ctmp = vb2xm*vb3x + vb2ym*vb3y + vb2zm*vb3z;
r12c2 = 1.0 / (b2mag*b3mag);
c2mag = ctmp * r12c2;
// cos and sin of 2 angles and final c
sin2 = MAX(1.0 - c1mag*c1mag,0.0);
sc1 = sqrt(sin2);
if (sc1 < SMALL) sc1 = SMALL;
sc1 = 1.0/sc1;
sin2 = MAX(1.0 - c2mag*c2mag,0.0);
sc2 = sqrt(sin2);
if (sc2 < SMALL) sc2 = SMALL;
sc2 = 1.0/sc2;
s1 = sc1 * sc1;
s2 = sc2 * sc2;
s12 = sc1 * sc2;
c = (c0 + c1mag*c2mag) * s12;
cx = vb1y*vb2z - vb1z*vb2y;
cy = vb1z*vb2x - vb1x*vb2z;
cz = vb1x*vb2y - vb1y*vb2x;
cmag = sqrt(cx*cx + cy*cy + cz*cz);
dx = (cx*vb3x + cy*vb3y + cz*vb3z)/cmag/b3mag;
// error check
if (c > 1.0 + TOLERANCE || c < (-1.0 - TOLERANCE)) {
if (screen) {
fprintf(screen,"Dihedral problem: %d %d %d %d %d %d\n",
comm->me,update->ntimestep,
atom->tag[i1],atom->tag[i2],atom->tag[i3],atom->tag[i4]);
fprintf(screen," 1st atom: %d %g %g %g\n",
comm->me,x[i1][0],x[i1][1],x[i1][2]);
fprintf(screen," 2nd atom: %d %g %g %g\n",
comm->me,x[i2][0],x[i2][1],x[i2][2]);
fprintf(screen," 3rd atom: %d %g %g %g\n",
comm->me,x[i3][0],x[i3][1],x[i3][2]);
fprintf(screen," 4th atom: %d %g %g %g\n",
comm->me,x[i4][0],x[i4][1],x[i4][2]);
}
}
if (c > 1.0) c = 1.0;
if (c < -1.0) c = -1.0;
// force & energy
// p = sum (i=1,4) k_i * (1 + (-1)**(i+1)*cos(i*phi) )
// pd = dp/dc
phi = acos(c);
if (dx < 0.0) phi *= -1.0;
si = sin(phi);
if (fabs(si) < SMALLER) si = SMALLER;
siinv = 1.0/si;
p = k1[type]*(1.0 + c) + k2[type]*(1.0 - cos(2.0*phi)) +
k3[type]*(1.0 + cos(3.0*phi)) + k4[type]*(1.0 - cos(4.0*phi)) ;
pd = k1[type] - 2.0*k2[type]*sin(2.0*phi)*siinv +
3.0*k3[type]*sin(3.0*phi)*siinv - 4.0*k4[type]*sin(4.0*phi)*siinv;
if (eflag) energy += rfactor * p;
a = pd;
c = c * a;
s12 = s12 * a;
a11 = -c*sb1*s1;
a22 = sb2 * (2.0*c0*s12 - c*(s1+s2));
a33 = -c*sb3*s2;
a12 = r12c1 * (c1mag*c*s1 + c2mag*s12);
a13 = rb1*rb3*s12;
a23 = r12c2 * (-c2mag*c*s2 - c1mag*s12);
sx1 = a11*vb1x + a12*vb2x + a13*vb3x;
sx2 = a12*vb1x + a22*vb2x + a23*vb3x;
sx12 = a13*vb1x + a23*vb2x + a33*vb3x;
sy1 = a11*vb1y + a12*vb2y + a13*vb3y;
sy2 = a12*vb1y + a22*vb2y + a23*vb3y;
sy12 = a13*vb1y + a23*vb2y + a33*vb3y;
sz1 = a11*vb1z + a12*vb2z + a13*vb3z;
sz2 = a12*vb1z + a22*vb2z + a23*vb3z;
sz12 = a13*vb1z + a23*vb2z + a33*vb3z;
// apply force to each of 4 atoms
if (newton_bond || i1 < nlocal) {
f[i1][0] -= sx1;
f[i1][1] -= sy1;
f[i1][2] -= sz1;
}
if (newton_bond || i2 < nlocal) {
f[i2][0] += sx2 + sx1;
f[i2][1] += sy2 + sy1;
f[i2][2] += sz2 + sz1;
}
if (newton_bond || i3 < nlocal) {
f[i3][0] += sx12 - sx2;
f[i3][1] += sy12 - sy2;
f[i3][2] += sz12 - sz2;
}
if (newton_bond || i4 < nlocal) {
f[i4][0] -= sx12;
f[i4][1] -= sy12;
f[i4][2] -= sz12;
}
// virial contribution
if (vflag) {
virial[0] -= rfactor * (vb1x*sx1 + vb2x*sx2 + vb3x*sx12);
virial[1] -= rfactor * (vb1y*sy1 + vb2y*sy2 + vb3y*sy12);
virial[2] -= rfactor * (vb1z*sz1 + vb2z*sz2 + vb3z*sz12);
virial[3] -= rfactor * (vb1x*sy1 + vb2x*sy2 + vb3x*sy12);
virial[4] -= rfactor * (vb1x*sz1 + vb2x*sz2 + vb3x*sz12);
virial[5] -= rfactor * (vb1y*sz1 + vb2y*sz2 + vb3y*sz12);
}
}
}
/* ---------------------------------------------------------------------- */
void DihedralOPLS::allocate()
{
allocated = 1;
int n = atom->ndihedraltypes;
k1 = (double *) memory->smalloc((n+1)*sizeof(double),"dihedral:k1");
k2 = (double *) memory->smalloc((n+1)*sizeof(double),"dihedral:k2");
k3 = (double *) memory->smalloc((n+1)*sizeof(double),"dihedral:k3");
k4 = (double *) memory->smalloc((n+1)*sizeof(double),"dihedral:k4");
setflag = (int *) memory->smalloc((n+1)*sizeof(int),"dihedral:setflag");
for (int i = 1; i <= n; i++) setflag[i] = 0;
}
/* ----------------------------------------------------------------------
set coeffs for one type
------------------------------------------------------------------------- */
void DihedralOPLS::coeff(int which, int narg, char **arg)
{
if (which != 0) error->all("Invalid coeffs for this dihedral style");
if (narg != 5) error->all("Incorrect args for dihedral coefficients");
if (!allocated) allocate();
int ilo,ihi;
force->bounds(arg[0],atom->ndihedraltypes,ilo,ihi);
double k1_one = atof(arg[1]);
double k2_one = atof(arg[2]);
double k3_one = atof(arg[3]);
double k4_one = atof(arg[4]);
// store 1/2 factor with prefactor
int count = 0;
for (int i = ilo; i <= ihi; i++) {
k1[i] = 0.5*k1_one;
k2[i] = 0.5*k2_one;
k3[i] = 0.5*k3_one;
k4[i] = 0.5*k4_one;
setflag[i] = 1;
count++;
}
if (count == 0) error->all("Incorrect args for dihedral coefficients");
}
/* ----------------------------------------------------------------------
proc 0 writes out coeffs to restart file
------------------------------------------------------------------------- */
void DihedralOPLS::write_restart(FILE *fp)
{
fwrite(&k1[1],sizeof(double),atom->ndihedraltypes,fp);
fwrite(&k2[1],sizeof(double),atom->ndihedraltypes,fp);
fwrite(&k3[1],sizeof(double),atom->ndihedraltypes,fp);
fwrite(&k4[1],sizeof(double),atom->ndihedraltypes,fp);
}
/* ----------------------------------------------------------------------
proc 0 reads coeffs from restart file, bcasts them
------------------------------------------------------------------------- */
void DihedralOPLS::read_restart(FILE *fp)
{
allocate();
if (comm->me == 0) {
fread(&k1[1],sizeof(double),atom->ndihedraltypes,fp);
fread(&k2[1],sizeof(double),atom->ndihedraltypes,fp);
fread(&k3[1],sizeof(double),atom->ndihedraltypes,fp);
fread(&k4[1],sizeof(double),atom->ndihedraltypes,fp);
}
MPI_Bcast(&k1[1],atom->ndihedraltypes,MPI_DOUBLE,0,world);
MPI_Bcast(&k2[1],atom->ndihedraltypes,MPI_DOUBLE,0,world);
MPI_Bcast(&k3[1],atom->ndihedraltypes,MPI_DOUBLE,0,world);
MPI_Bcast(&k4[1],atom->ndihedraltypes,MPI_DOUBLE,0,world);
for (int i = 1; i <= atom->ndihedraltypes; i++) setflag[i] = 1;
}
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