180 lines
4.8 KiB
C++
180 lines
4.8 KiB
C++
/* ----------------------------------------------------------------------
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LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
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http://lammps.sandia.gov, Sandia National Laboratories
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Steve Plimpton, sjplimp@sandia.gov
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This software is distributed under the GNU General Public License.
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See the README file in the top-level LAMMPS directory.
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------------------------------------------------------------------------- */
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/* ----------------------------------------------------------------------
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Contributing author: Axel Kohlmeyer (U Penn), akohlmey at cmm.chem.upenn.edu
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------------------------------------------------------------------------- */
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#include "math.h"
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#include "stdlib.h"
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#include "angle_cosine_delta.h"
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#include "atom.h"
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#include "neighbor.h"
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#include "domain.h"
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#include "comm.h"
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#include "force.h"
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#include "memory.h"
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#include "error.h"
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using namespace LAMMPS_NS;
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#define SMALL 0.001
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/* ---------------------------------------------------------------------- */
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AngleCosineDelta::AngleCosineDelta(LAMMPS *lmp) : AngleCosineSquared(lmp) {}
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/* ---------------------------------------------------------------------- */
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void AngleCosineDelta::compute(int eflag, int vflag)
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{
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int i1,i2,i3,n,type;
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double delx1,dely1,delz1,delx2,dely2,delz2,theta,dtheta,dcostheta,tk;
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double eangle,f1[3],f3[3];
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double rsq1,rsq2,r1,r2,c,a,cot,a11,a12,a22,b11,b12,b22,c0,s0,s;
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eangle = 0.0;
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if (eflag || vflag) ev_setup(eflag,vflag);
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else evflag = 0;
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double **x = atom->x;
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double **f = atom->f;
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int **anglelist = neighbor->anglelist;
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int nanglelist = neighbor->nanglelist;
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int nlocal = atom->nlocal;
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int newton_bond = force->newton_bond;
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for (n = 0; n < nanglelist; n++) {
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i1 = anglelist[n][0];
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i2 = anglelist[n][1];
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i3 = anglelist[n][2];
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type = anglelist[n][3];
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// 1st bond
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delx1 = x[i1][0] - x[i2][0];
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dely1 = x[i1][1] - x[i2][1];
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delz1 = x[i1][2] - x[i2][2];
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domain->minimum_image(delx1,dely1,delz1);
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rsq1 = delx1*delx1 + dely1*dely1 + delz1*delz1;
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r1 = sqrt(rsq1);
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// 2nd bond
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delx2 = x[i3][0] - x[i2][0];
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dely2 = x[i3][1] - x[i2][1];
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delz2 = x[i3][2] - x[i2][2];
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domain->minimum_image(delx2,dely2,delz2);
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rsq2 = delx2*delx2 + dely2*dely2 + delz2*delz2;
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r2 = sqrt(rsq2);
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// angle (cos and sin)
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c = delx1*delx2 + dely1*dely2 + delz1*delz2;
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c /= r1*r2;
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if (c > 1.0) c = 1.0;
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if (c < -1.0) c = -1.0;
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theta = acos(c);
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s = sqrt(1.0 - c*c);
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if (s < SMALL) s = SMALL;
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s = 1.0/s;
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cot = c/s;
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// force & energy
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dtheta = theta - theta0[type];
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dcostheta = cos(dtheta);
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tk = k[type] * (1.0-dcostheta);
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if (eflag) eangle = tk;
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a = -k[type];
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// expand dtheta for cos and sin contribution to force
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a11 = a*c / rsq1;
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a12 = -a / (r1*r2);
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a22 = a*c / rsq2;
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b11 = -a*c*cot / rsq1;
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b12 = a*cot / (r1*r2);
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b22 = -a*c*cot / rsq2;
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c0 = cos(theta0[type]);
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s0 = sin(theta0[type]);
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f1[0] = (a11*delx1 + a12*delx2)*c0 + (b11*delx1 + b12*delx2)*s0;
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f1[1] = (a11*dely1 + a12*dely2)*c0 + (b11*dely1 + b12*dely2)*s0;
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f1[2] = (a11*delz1 + a12*delz2)*c0 + (b11*delz1 + b12*delz2)*s0;
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f3[0] = (a22*delx2 + a12*delx1)*c0 + (b22*delx2 + b12*delx1)*s0;
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f3[1] = (a22*dely2 + a12*dely1)*c0 + (b22*dely2 + b12*dely1)*s0;
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f3[2] = (a22*delz2 + a12*delz1)*c0 + (b22*delz2 + b12*delz1)*s0;
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// apply force to each of 3 atoms
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if (newton_bond || i1 < nlocal) {
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f[i1][0] += f1[0];
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f[i1][1] += f1[1];
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f[i1][2] += f1[2];
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}
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if (newton_bond || i2 < nlocal) {
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f[i2][0] -= f1[0] + f3[0];
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f[i2][1] -= f1[1] + f3[1];
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f[i2][2] -= f1[2] + f3[2];
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}
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if (newton_bond || i3 < nlocal) {
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f[i3][0] += f3[0];
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f[i3][1] += f3[1];
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f[i3][2] += f3[2];
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}
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if (evflag) ev_tally(i1,i2,i3,nlocal,newton_bond,eangle,f1,f3,
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delx1,dely1,delz1,delx2,dely2,delz2);
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}
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}
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/* ---------------------------------------------------------------------- */
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double AngleCosineDelta::single(int type, int i1, int i2, int i3)
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{
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double **x = atom->x;
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double delx1 = x[i1][0] - x[i2][0];
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double dely1 = x[i1][1] - x[i2][1];
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double delz1 = x[i1][2] - x[i2][2];
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domain->minimum_image(delx1,dely1,delz1);
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double r1 = sqrt(delx1*delx1 + dely1*dely1 + delz1*delz1);
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double delx2 = x[i3][0] - x[i2][0];
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double dely2 = x[i3][1] - x[i2][1];
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double delz2 = x[i3][2] - x[i2][2];
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domain->minimum_image(delx2,dely2,delz2);
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double r2 = sqrt(delx2*delx2 + dely2*dely2 + delz2*delz2);
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double c = delx1*delx2 + dely1*dely2 + delz1*delz2;
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c /= r1*r2;
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if (c > 1.0) c = 1.0;
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if (c < -1.0) c = -1.0;
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double theta = acos(c);
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double dtheta = theta - theta0[type];
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double dcostheta = cos(dtheta);
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double tk = k[type] * (1.0-dcostheta);
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return tk;
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}
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