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lammps/src/fix_nh_sphere.cpp
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fix_nh_sphere.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: Mike Brown (SNL)
------------------------------------------------------------------------- */
#include <math.h>
#include "fix_nh_sphere.h"
#include "atom.h"
#include "atom_vec.h"
#include "group.h"
#include "error.h"
#include "force.h"
#include "domain.h"
#include "math_vector.h"
#include "math_extra.h"
using namespace LAMMPS_NS;
using namespace FixConst;
using namespace MathExtra;
/* ---------------------------------------------------------------------- */
FixNHSphere::FixNHSphere(LAMMPS *lmp, int narg, char **arg) :
FixNH(lmp, narg, arg)
{
if (!atom->sphere_flag)
error->all(FLERR,"Fix nvt/nph/npt sphere requires atom style sphere");
// inertia = moment of inertia prefactor for sphere or disc
inertia = 0.4;
int iarg = 3;
while (iarg < narg) {
if (strcmp(arg[iarg],"disc") == 0){
inertia = 0.5;
if (domain->dimension != 2)
error->all(FLERR,
"Fix nvt/nph/npt sphere disc option requires 2d simulation");
}
iarg++;
}
}
/* ---------------------------------------------------------------------- */
void FixNHSphere::init()
{
// check that all particles are finite-size
// no point particles allowed
double *radius = atom->radius;
int *mask = atom->mask;
int nlocal = atom->nlocal;
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit)
if (radius[i] == 0.0)
error->one(FLERR,"Fix nvt/npt/nph/sphere require extended particles");
FixNH::init();
}
/* ----------------------------------------------------------------------
perform half-step update of rotational velocities
-----------------------------------------------------------------------*/
void FixNHSphere::nve_v()
{
// standard nve_v velocity update
FixNH::nve_v();
double **omega = atom->omega;
double **torque = atom->torque;
double *radius = atom->radius;
double *rmass = atom->rmass;
int *mask = atom->mask;
int nlocal = atom->nlocal;
if (igroup == atom->firstgroup) nlocal = atom->nfirst;
// set timestep here since dt may have changed or come via rRESPA
double dtfrotate = dtf / inertia;
double dtirotate;
// update omega for all particles
// d_omega/dt = torque / inertia
// 4 cases depending on radius vs shape and rmass vs mass
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit) {
dtirotate = dtfrotate / (radius[i]*radius[i]*rmass[i]);
omega[i][0] += dtirotate*torque[i][0];
omega[i][1] += dtirotate*torque[i][1];
omega[i][2] += dtirotate*torque[i][2];
}
}
/* ----------------------------------------------------------------------
perform full-step update of position with dipole orientation, if requested
-----------------------------------------------------------------------*/
void FixNHSphere::nve_x()
{
// standard nve_x position update
FixNH::nve_x();
// update mu for dipoles
if (dipole_flag) {
double **mu = atom->mu;
double **omega = atom->omega;
int *mask = atom->mask;
int nlocal = atom->nlocal;
if (dlm_flag == 0){
// d_mu/dt = omega cross mu
// renormalize mu to dipole length
double msq,scale,g[3];
for (int i = 0; i < nlocal; i++)
if (mask[i] & groupbit)
if (mu[i][3] > 0.0) {
g[0] = mu[i][0] + dtv * (omega[i][1]*mu[i][2]-omega[i][2]*mu[i][1]);
g[1] = mu[i][1] + dtv * (omega[i][2]*mu[i][0]-omega[i][0]*mu[i][2]);
g[2] = mu[i][2] + dtv * (omega[i][0]*mu[i][1]-omega[i][1]*mu[i][0]);
msq = g[0]*g[0] + g[1]*g[1] + g[2]*g[2];
scale = mu[i][3]/sqrt(msq);
mu[i][0] = g[0]*scale;
mu[i][1] = g[1]*scale;
mu[i][2] = g[2]*scale;
}
} else {
// Integrate orientation following Dullweber-Leimkuhler-Maclachlan scheme
vector w, w_temp, a;
matrix Q, Q_temp, R;
double scale,s2,inv_len_mu;
for (int i = 0; i < nlocal; i++) {
if (mask[i] & groupbit && mu[i][3] > 0.0) {
// Construct Q from dipole:
// Q is the rotation matrix from space frame to body frame
// i.e. v_b = Q.v_s
// Define mu to lie along the z axis in the body frame
// We take the unit dipole to avoid getting a scaling matrix
inv_len_mu = 1.0/mu[i][3];
a[0] = mu[i][0]*inv_len_mu;
a[1] = mu[i][1]*inv_len_mu;
a[2] = mu[i][2]*inv_len_mu;
// v = a x [0 0 1] - cross product of mu in space and body frames
// s = |v|
// c = a.[0 0 1] = a[2]
// vx = [ 0 -v[2] v[1]
// v[2] 0 -v[0]
// -v[1] v[0] 0 ]
// then
// Q = I + vx + vx^2 * (1-c)/s^2
s2 = a[0]*a[0] + a[1]*a[1];
if (s2 != 0.0){ // i.e. the vectors are not parallel
scale = (1.0 - a[2])/s2;
Q[0][0] = 1.0 - scale*a[0]*a[0]; Q[0][1] = -scale*a[0]*a[1]; Q[0][2] = -a[0];
Q[1][0] = -scale*a[0]*a[1]; Q[1][1] = 1.0 - scale*a[1]*a[1]; Q[1][2] = -a[1];
Q[2][0] = a[0]; Q[2][1] = a[1]; Q[2][2] = 1.0 - scale*(a[0]*a[0] + a[1]*a[1]);
} else { // if parallel then we just have I or -I
Q[0][0] = 1.0/a[2]; Q[0][1] = 0.0; Q[0][2] = 0.0;
Q[1][0] = 0.0; Q[1][1] = 1.0/a[2]; Q[1][2] = 0.0;
Q[2][0] = 0.0; Q[2][1] = 0.0; Q[2][2] = 1.0/a[2];
}
// Local copy of this particle's angular velocity (in space frame)
w[0] = omega[i][0]; w[1] = omega[i][1]; w[2] = omega[i][2];
// Transform omega into body frame: w_temp= Q.w
matvec(Q,w,w_temp);
// Construct rotation R1
BuildRxMatrix(R, dtf/force->ftm2v*w_temp[0]);
// Apply R1 to w: w = R.w_temp
matvec(R,w_temp,w);
// Apply R1 to Q: Q_temp = R^T.Q
transpose_times3(R,Q,Q_temp);
// Construct rotation R2
BuildRyMatrix(R, dtf/force->ftm2v*w[1]);
// Apply R2 to w: w_temp = R.w
matvec(R,w,w_temp);
// Apply R2 to Q: Q = R^T.Q_temp
transpose_times3(R,Q_temp,Q);
// Construct rotation R3
BuildRzMatrix(R, 2.0*dtf/force->ftm2v*w_temp[2]);
// Apply R3 to w: w = R.w_temp
matvec(R,w_temp,w);
// Apply R3 to Q: Q_temp = R^T.Q
transpose_times3(R,Q,Q_temp);
// Construct rotation R4
BuildRyMatrix(R, dtf/force->ftm2v*w[1]);
// Apply R4 to w: w_temp = R.w
matvec(R,w,w_temp);
// Apply R4 to Q: Q = R^T.Q_temp
transpose_times3(R,Q_temp,Q);
// Construct rotation R5
BuildRxMatrix(R, dtf/force->ftm2v*w_temp[0]);
// Apply R5 to w: w = R.w_temp
matvec(R,w_temp,w);
// Apply R5 to Q: Q_temp = R^T.Q
transpose_times3(R,Q,Q_temp);
// Transform w back into space frame w_temp = Q^T.w
transpose_matvec(Q_temp,w,w_temp);
omega[i][0] = w_temp[0]; omega[i][1] = w_temp[1]; omega[i][2] = w_temp[2];
// Set dipole according to updated Q: mu = Q^T.[0 0 1] * |mu|
mu[i][0] = Q_temp[2][0] * mu[i][3];
mu[i][1] = Q_temp[2][1] * mu[i][3];
mu[i][2] = Q_temp[2][2] * mu[i][3];
}
}
}
}
}
/* ----------------------------------------------------------------------
perform half-step scaling of rotatonal velocities
-----------------------------------------------------------------------*/
void FixNHSphere::nh_v_temp()
{
// standard nh_v_temp scaling
FixNH::nh_v_temp();
double **omega = atom->omega;
int *mask = atom->mask;
int nlocal = atom->nlocal;
if (igroup == atom->firstgroup) nlocal = atom->nfirst;
for (int i = 0; i < nlocal; i++) {
if (mask[i] & groupbit) {
omega[i][0] *= factor_eta;
omega[i][1] *= factor_eta;
omega[i][2] *= factor_eta;
}
}
}
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