283 lines
7.6 KiB
C++
283 lines
7.6 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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Copyright (2003) Sandia Corporation. Under the terms of Contract
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DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
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certain rights in this software. This software is distributed under
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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 authors: Julien Tranchida (SNL)
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Aidan Thompson (SNL)
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Please cite the related publication:
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Tranchida, J., Plimpton, S. J., Thibaudeau, P., & Thompson, A. P. (2018).
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Massively parallel symplectic algorithm for coupled magnetic spin dynamics
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and molecular dynamics. Journal of Computational Physics.
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------------------------------------------------------------------------- */
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#include <cmath>
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#include <cstdio>
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#include <cstdlib>
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#include <cstring>
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#include "atom.h"
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#include "domain.h"
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#include "error.h"
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#include "fix_precession_spin.h"
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#include "force.h"
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#include "input.h"
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#include "math_const.h"
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#include "memory.h"
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#include "modify.h"
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#include "respa.h"
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#include "update.h"
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#include "variable.h"
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using namespace LAMMPS_NS;
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using namespace FixConst;
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using namespace MathConst;
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enum{CONSTANT,EQUAL};
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/* ---------------------------------------------------------------------- */
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FixPrecessionSpin::FixPrecessionSpin(LAMMPS *lmp, int narg, char **arg) : Fix(lmp, narg, arg)
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{
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if (narg < 7) error->all(FLERR,"Illegal precession/spin command");
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// magnetic interactions coded for cartesian coordinates
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hbar = force->hplanck/MY_2PI;
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dynamic_group_allow = 1;
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scalar_flag = 1;
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global_freq = 1;
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extscalar = 1;
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respa_level_support = 1;
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ilevel_respa = 0;
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magstr = NULL;
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magfieldstyle = CONSTANT;
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H_field = 0.0;
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nhx = nhy = nhz = 0.0;
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hx = hy = hz = 0.0;
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Ka = 0.0;
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nax = nay = naz = 0.0;
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Kax = Kay = Kaz = 0.0;
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zeeman_flag = aniso_flag = 0;
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int iarg = 3;
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while (iarg < narg) {
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if (strcmp(arg[iarg],"zeeman") == 0) {
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if (iarg+4 > narg) error->all(FLERR,"Illegal fix precession/spin command");
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zeeman_flag = 1;
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H_field = force->numeric(FLERR,arg[iarg+1]);
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nhx = force->numeric(FLERR,arg[iarg+2]);
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nhy = force->numeric(FLERR,arg[iarg+3]);
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nhz = force->numeric(FLERR,arg[iarg+4]);
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iarg += 5;
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} else if (strcmp(arg[iarg],"anisotropy") == 0) {
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if (iarg+4 > narg) error->all(FLERR,"Illegal fix precession/spin command");
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aniso_flag = 1;
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Ka = force->numeric(FLERR,arg[iarg+1]);
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nax = force->numeric(FLERR,arg[iarg+2]);
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nay = force->numeric(FLERR,arg[iarg+3]);
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naz = force->numeric(FLERR,arg[iarg+4]);
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iarg += 5;
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} else error->all(FLERR,"Illegal precession/spin command");
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}
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degree2rad = MY_PI/180.0;
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time_origin = update->ntimestep;
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eflag = 0;
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emag = 0.0;
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}
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/* ---------------------------------------------------------------------- */
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FixPrecessionSpin::~FixPrecessionSpin()
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{
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delete [] magstr;
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}
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/* ---------------------------------------------------------------------- */
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int FixPrecessionSpin::setmask()
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{
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int mask = 0;
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mask |= POST_FORCE;
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mask |= THERMO_ENERGY;
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mask |= POST_FORCE_RESPA;
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return mask;
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}
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/* ---------------------------------------------------------------------- */
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void FixPrecessionSpin::init()
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{
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const double hbar = force->hplanck/MY_2PI; // eV/(rad.THz)
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const double mub = 5.78901e-5; // in eV/T
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const double gyro = mub/hbar; // in rad.THz/T
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H_field *= gyro; // in rad.THz
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Ka /= hbar; // in rad.THz
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if (strstr(update->integrate_style,"respa")) {
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ilevel_respa = ((Respa *) update->integrate)->nlevels-1;
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if (respa_level >= 0) ilevel_respa = MIN(respa_level,ilevel_respa);
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}
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if (magstr) {
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magvar = input->variable->find(magstr);
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if (magvar < 0)
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error->all(FLERR,"Illegal precession/spin command");
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if (!input->variable->equalstyle(magvar))
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error->all(FLERR,"Illegal precession/spin command");
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}
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varflag = CONSTANT;
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if (magfieldstyle != CONSTANT) varflag = EQUAL;
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// set magnetic field components
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if (varflag == CONSTANT) set_magneticprecession();
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}
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/* ---------------------------------------------------------------------- */
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void FixPrecessionSpin::setup(int vflag)
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{
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if (strstr(update->integrate_style,"verlet"))
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post_force(vflag);
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else {
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((Respa *) update->integrate)->copy_flevel_f(ilevel_respa);
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post_force_respa(vflag,ilevel_respa,0);
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((Respa *) update->integrate)->copy_f_flevel(ilevel_respa);
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}
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}
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/* ---------------------------------------------------------------------- */
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void FixPrecessionSpin::post_force(int /*vflag*/)
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{
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// update mag field with time (potential improvement)
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if (varflag != CONSTANT) {
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modify->clearstep_compute();
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modify->addstep_compute(update->ntimestep + 1);
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set_magneticprecession(); // update mag. field if time-dep.
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}
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double **sp = atom->sp;
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double **fm = atom->fm;
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double spi[3], fmi[3];
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const int nlocal = atom->nlocal;
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eflag = 0;
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emag = 0.0;
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for (int i = 0; i < nlocal; i++) {
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spi[0] = sp[i][0];
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spi[1] = sp[i][1];
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spi[2] = sp[i][2];
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fmi[0] = fmi[1] = fmi[2] = 0.0;
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if (zeeman_flag) { // compute Zeeman interaction
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compute_zeeman(i,fmi);
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emag -= (spi[0]*fmi[0] + spi[1]*fmi[1] + spi[2]*fmi[2]);
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}
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if (aniso_flag) { // compute magnetic anisotropy
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compute_anisotropy(spi,fmi);
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emag -= (spi[0]*fmi[0] + spi[1]*fmi[1] + spi[2]*fmi[2]);
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}
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fm[i][0] += fmi[0];
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fm[i][1] += fmi[1];
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fm[i][2] += fmi[2];
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}
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emag *= hbar;
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}
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/* ---------------------------------------------------------------------- */
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void FixPrecessionSpin::compute_single_precession(int i, double spi[3], double fmi[3])
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{
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if (zeeman_flag) {
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compute_zeeman(i,fmi);
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}
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if (aniso_flag) {
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compute_anisotropy(spi,fmi);
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}
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}
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/* ---------------------------------------------------------------------- */
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void FixPrecessionSpin::compute_zeeman(int i, double fmi[3])
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{
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double **sp = atom->sp;
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fmi[0] -= sp[i][3]*hx;
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fmi[1] -= sp[i][3]*hy;
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fmi[2] -= sp[i][3]*hz;
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}
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/* ---------------------------------------------------------------------- */
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void FixPrecessionSpin::compute_anisotropy(double spi[3], double fmi[3])
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{
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double scalar = nax*spi[0] + nay*spi[1] + naz*spi[2];
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fmi[0] += scalar*Kax;
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fmi[1] += scalar*Kay;
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fmi[2] += scalar*Kaz;
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}
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/* ---------------------------------------------------------------------- */
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void FixPrecessionSpin::post_force_respa(int vflag, int ilevel, int /*iloop*/)
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{
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if (ilevel == ilevel_respa) post_force(vflag);
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}
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/* ---------------------------------------------------------------------- */
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void FixPrecessionSpin::set_magneticprecession()
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{
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if (zeeman_flag) {
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hx = H_field*nhx;
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hy = H_field*nhy;
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hz = H_field*nhz;
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}
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if (aniso_flag) {
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Kax = 2.0*Ka*nax;
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Kay = 2.0*Ka*nay;
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Kaz = 2.0*Ka*naz;
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}
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}
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/* ----------------------------------------------------------------------
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potential energy in magnetic field
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------------------------------------------------------------------------- */
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double FixPrecessionSpin::compute_scalar()
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{
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// only sum across procs one time
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if (eflag == 0) {
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MPI_Allreduce(&emag,&emag_all,1,MPI_DOUBLE,MPI_SUM,world);
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eflag = 1;
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}
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return emag_all;
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}
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