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Merge pull request #2714 from julient31/STT2

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Improvement of the SPIN package by removing a limitation
This commit is contained in:
Axel Kohlmeyer
2021-04-21 14:55:17 -04:00
committed by GitHub
parent 2e01bb8f62 6cad2ba829
commit a64a7d5096
11 changed files with 389 additions and 73 deletions
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34
doc/src/fix_precession_spin.rst
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@ -12,7 +12,7 @@ Syntax
* ID, group are documented in :doc:`fix <fix>` command
* precession/spin = style name of this fix command
* style = *zeeman* or *anisotropy* or *cubic*
* style = *zeeman* or *anisotropy* or *cubic* or *stt*
.. parsed-literal::
@ -22,12 +22,12 @@ Syntax
*anisotropy* args = K x y z
K = intensity of the magnetic anisotropy (in eV)
x y z = vector direction of the anisotropy
.. parsed-literal::
*cubic* args = K1 K2c n1x n1y n1x n2x n2y n2z n3x n3y n3z
K1 and K2c = intensity of the magnetic anisotropy (in eV)
n1x to n3z = three direction vectors of the cubic anisotropy
*stt* args = J x y z
J = intensity of the spin-transfer torque field
x y z = vector direction of the field
Examples
""""""""
@ -125,6 +125,11 @@ axis along the :math:`(1 1 1)`-type cube diagonals). :math:`K_2^c >
diagonals. See chapter 2 of :ref:`(Skomski) <Skomski1>` for more
details on cubic anisotropies.
Style *stt* is used to simulate the interaction between the spins and
a spin-transfer torque.
See equation (7) of :ref:`(Chirac) <Chirac1>` for more details about the
implemented spin-transfer torque term.
In all cases, the choice of :math:`(x y z)` only imposes the vector
directions for the forces. Only the direction of the vector is
important; its length is ignored (the entered vectors are
@ -132,6 +137,16 @@ normalized).
Those styles can be combined within one single command line.
.. note::
The norm of all vectors defined with the precession/spin command
have to be non-zero. For example, defining
"fix 1 all precession/spin zeeman 0.1 0.0 0.0 0.0" would result
in an error message.
Since those vector components are used to compute the inverse of the
field (or anisotropy) vector norm, setting a zero-vector would result
in a division by zero.
----------
Restart, fix_modify, output, run start/stop, minimize info
@ -162,11 +177,6 @@ is only enabled if LAMMPS was built with this package, and if the
atom_style "spin" was declared. See the :doc:`Build package
<Build_package>` doc page for more info.
The *precession/spin* style can only be declared once. If more than
one precession type (for example combining an anisotropy and a Zeeman
interactions) has to be declared, they have to be chained in the same
command line (as shown in the examples above).
Related commands
""""""""""""""""
@ -184,3 +194,9 @@ none
**(Skomski)** Skomski, R. (2008). Simple models of magnetism.
Oxford University Press.
.. _Chirac1:
**(Chirac)** Chirac, Théophile, et al. Ultrafast antiferromagnetic
switching in NiO induced by spin transfer torques.
Physical Review B 102.13 (2020): 134415.

11
examples/SPIN/test_problems/README
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@ -45,3 +45,14 @@ directory.
results (computed by the python script).
Note: This example is a reworked version of a test problem
provided by Martin Kroger (ETHZ).
- validation_nve:
simulates a small assembly of magnetic atoms (54). The atoms are
coupled by an exchange interaction and a mechanical potential
(EAM here).
This example represents an NVE run: the total energy of the
system is preserved, whereas the spin and lattice energy
reservoirs are exchanging energy.
Run as: ./run-test-nve.sh
Output: res_lammps.dat contains the data. The results are displayed
by nve_spin_lattice.pdf.

25
examples/SPIN/test_problems/run_all.sh Executable file
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@ -0,0 +1,25 @@
#!/bin/bash
# test 1: damping and exchange
cd validation_damped_exchange/
./run-test-exchange.sh
rm dump.data res_lammps.dat res_llg.dat
cd ..
# test 2: damping and Zeeman
cd validation_damped_precession/
./run-test-prec.sh
rm res_lammps.dat res_llg.dat
cd ..
# test 3: langevin, damping and Zeeman
cd validation_langevin_precession/
./run-test-prec.sh
rm average_spin test-prec-spin.in res_lammps.dat res_langevin.dat
cd ..
# test 4: NVE run, test Etot preservation
cd validation_nve/
./run-test-nve.sh
rm nve_spin_lattice.pdf res_lammps.dat
cd ..

4
examples/SPIN/test_problems/validation_nvt/in.spin.nvt_lattice
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@ -31,8 +31,8 @@ neighbor 0.1 bin
neigh_modify every 10 check yes delay 20
fix 1 all precession/spin zeeman 0.0 0.0 0.0 1.0
fix 2 all langevin 200.0 200.0 1.0 48279
fix 3 all langevin/spin 0.0 0.00001 321
fix 2 all langevin 200.0 200.0 0.1 48279
fix 3 all langevin/spin 0.0 0.0 321
fix 4 all nve/spin lattice moving
timestep 0.001

9
examples/SPIN/test_problems/validation_nvt/in.spin.nvt_spin
View File

@ -22,16 +22,19 @@ mass 1 55.845
set group all spin 2.2 0.0 0.0 1.0
velocity all create 0 4928459 rot yes dist gaussian
pair_style hybrid/overlay eam/alloy spin/exchange 3.5
# pair_style hybrid/overlay eam/alloy spin/exchange 3.5
pair_style hybrid/overlay eam/alloy spin/exchange 4.0 spin/neel 4.0
pair_coeff * * eam/alloy Fe_Mishin2006.eam.alloy Fe
pair_coeff * * spin/exchange exchange 3.4 0.1 0.2171 1.841
pair_coeff * * spin/neel neel 4.0 0.02 0.0 1.841 0.0 0.0 1.0
neighbor 0.1 bin
neigh_modify every 10 check yes delay 20
fix 1 all precession/spin zeeman 0.0 0.0 0.0 1.0
fix 2 all langevin/spin 200.0 0.01 321
fix 3 all nve/spin lattice moving
fix 2 all langevin 0.0 0.0 0.0 48279
fix 3 all langevin/spin 200.0 0.01 321
fix 4 all nve/spin lattice moving
timestep 0.001
# compute and output options

20
src/SPIN/fix_langevin_spin.cpp
View File

@ -24,9 +24,11 @@
#include "fix_langevin_spin.h"
#include <cmath>
#include <cstring>
#include "atom.h"
#include "comm.h"
#include "error.h"
#include "force.h"
#include "group.h"
#include "math_const.h"
#include "memory.h"
#include "modify.h"
@ -42,7 +44,7 @@ using namespace MathConst;
/* ---------------------------------------------------------------------- */
FixLangevinSpin::FixLangevinSpin(LAMMPS *lmp, int narg, char **arg) :
Fix(lmp, narg, arg), id_temp(nullptr), random(nullptr)
Fix(lmp, narg, arg), random(nullptr)
{
if (narg != 6) error->all(FLERR,"Illegal langevin/spin command");
@ -106,10 +108,8 @@ void FixLangevinSpin::init()
double hbar = force->hplanck/MY_2PI; // eV/(rad.THz)
double kb = force->boltz; // eV/K
// D = (MY_2PI*alpha_t*gil_factor*kb*temp);
D = (alpha_t*gil_factor*kb*temp);
// D = (12.0/MY_2PI)*(MY_2PI*alpha_t*gil_factor*kb*temp);
D /= (hbar*dts);
sigma = sqrt(2.0*D);
}
@ -142,7 +142,7 @@ void FixLangevinSpin::add_tdamping(double spi[3], double fmi[3])
/* ---------------------------------------------------------------------- */
void FixLangevinSpin::add_temperature(double fmi[3])
void FixLangevinSpin::add_temperature(int i, double spi[3], double fmi[3])
{
// double rx = sigma*(2.0*random->uniform() - 1.0);
// double ry = sigma*(2.0*random->uniform() - 1.0);
@ -150,6 +150,7 @@ void FixLangevinSpin::add_temperature(double fmi[3])
double rx = sigma*random->gaussian();
double ry = sigma*random->gaussian();
double rz = sigma*random->gaussian();
double hbar = force->hplanck/MY_2PI;
// adding the random field
@ -163,3 +164,14 @@ void FixLangevinSpin::add_temperature(double fmi[3])
fmi[1] *= gil_factor;
fmi[2] *= gil_factor;
}
/* ---------------------------------------------------------------------- */
void FixLangevinSpin::compute_single_langevin(int i, double spi[3], double fmi[3])
{
int *mask = atom->mask;
if (mask[i] & groupbit) {
if (tdamp_flag) add_tdamping(spi,fmi);
if (temp_flag) add_temperature(i,spi,fmi);
}
}

8
src/SPIN/fix_langevin_spin.h
View File

@ -26,7 +26,7 @@ namespace LAMMPS_NS {
class FixLangevinSpin : public Fix {
public:
int tdamp_flag,ldamp_flag,temp_flag; // damping and temperature flags
int tdamp_flag,temp_flag; // damping and temperature flags
FixLangevinSpin(class LAMMPS *, int, char **);
virtual ~FixLangevinSpin();
@ -34,7 +34,8 @@ class FixLangevinSpin : public Fix {
void init();
void setup(int);
void add_tdamping(double *, double *); // add transverse damping
void add_temperature(double *); // add temperature
void add_temperature(int, double *, double *);
void compute_single_langevin(int, double *, double *);
protected:
double alpha_t; // transverse mag. damping
@ -43,9 +44,6 @@ class FixLangevinSpin : public Fix {
double D,sigma; // bath intensity var.
double gil_factor; // gilbert's prefactor
char *id_temp;
class Compute *temperature;
int nlevels_respa;
class RanMars *random;
int seed;

90
src/SPIN/fix_nve_spin.cpp
View File

@ -60,7 +60,8 @@ enum{NONE};
FixNVESpin::FixNVESpin(LAMMPS *lmp, int narg, char **arg) :
Fix(lmp, narg, arg),
pair(nullptr), spin_pairs(nullptr),
pair(nullptr), spin_pairs(nullptr), locklangevinspin(nullptr),
locksetforcespin(nullptr), lockprecessionspin(nullptr),
rsec(nullptr), stack_head(nullptr), stack_foot(nullptr),
backward_stacks(nullptr), forward_stacks(nullptr)
{
@ -75,6 +76,9 @@ FixNVESpin::FixNVESpin(LAMMPS *lmp, int narg, char **arg) :
npairs = 0;
npairspin = 0;
// test nprec
nprecspin = nlangspin = nsetspin = 0;
// checking if map array or hash is defined
if (atom->map_style == Atom::MAP_NONE)
@ -125,7 +129,6 @@ FixNVESpin::FixNVESpin(LAMMPS *lmp, int narg, char **arg) :
maglangevin_flag = 0;
tdamp_flag = temp_flag = 0;
setforce_spin_flag = 0;
}
/* ---------------------------------------------------------------------- */
@ -138,6 +141,8 @@ FixNVESpin::~FixNVESpin()
memory->destroy(forward_stacks);
memory->destroy(backward_stacks);
delete [] spin_pairs;
delete [] locklangevinspin;
delete [] lockprecessionspin;
}
/* ---------------------------------------------------------------------- */
@ -189,20 +194,20 @@ void FixNVESpin::init()
// loop 2: fill vector with ptrs to Pair/Spin styles
int count = 0;
int count1 = 0;
if (npairspin == 1) {
count = 1;
count1 = 1;
spin_pairs[0] = (PairSpin *) force->pair_match("spin",0,0);
} else if (npairspin > 1) {
for (int i = 0; i<npairs; i++) {
if (force->pair_match("spin",0,i)) {
spin_pairs[count] = (PairSpin *) force->pair_match("spin",0,i);
count++;
spin_pairs[count1] = (PairSpin *) force->pair_match("spin",0,i);
count1++;
}
}
}
if (count != npairspin)
if (count1 != npairspin)
error->all(FLERR,"Incorrect number of spin pairs");
// set pair/spin and long/spin flags
@ -215,30 +220,71 @@ void FixNVESpin::init()
}
}
// ptrs FixPrecessionSpin classes
// set ptrs for fix precession/spin styles
// loop 1: obtain # of fix precession/spin styles
int iforce;
for (iforce = 0; iforce < modify->nfix; iforce++) {
if (strstr(modify->fix[iforce]->style,"precession/spin")) {
precession_spin_flag = 1;
lockprecessionspin = (FixPrecessionSpin *) modify->fix[iforce];
nprecspin++;
}
}
// ptrs on the FixLangevinSpin class
// init length of vector of ptrs to precession/spin styles
if (nprecspin > 0) {
lockprecessionspin = new FixPrecessionSpin*[nprecspin];
}
// loop 2: fill vector with ptrs to precession/spin styles
int count2 = 0;
if (nprecspin > 0) {
for (iforce = 0; iforce < modify->nfix; iforce++) {
if (strstr(modify->fix[iforce]->style,"precession/spin")) {
precession_spin_flag = 1;
lockprecessionspin[count2] = (FixPrecessionSpin *) modify->fix[iforce];
count2++;
}
}
}
if (count2 != nprecspin)
error->all(FLERR,"Incorrect number of fix precession/spin");
// set ptrs for fix langevin/spin styles
// loop 1: obtain # of fix langevin/spin styles
for (iforce = 0; iforce < modify->nfix; iforce++) {
if (strstr(modify->fix[iforce]->style,"langevin/spin")) {
maglangevin_flag = 1;
locklangevinspin = (FixLangevinSpin *) modify->fix[iforce];
nlangspin++;
}
}
if (maglangevin_flag) {
if (locklangevinspin->tdamp_flag == 1) tdamp_flag = 1;
if (locklangevinspin->temp_flag == 1) temp_flag = 1;
// init length of vector of ptrs to precession/spin styles
if (nlangspin > 0) {
locklangevinspin = new FixLangevinSpin*[nprecspin];
}
// loop 2: fill vector with ptrs to precession/spin styles
count2 = 0;
if (nlangspin > 0) {
for (iforce = 0; iforce < modify->nfix; iforce++) {
if (strstr(modify->fix[iforce]->style,"langevin/spin")) {
maglangevin_flag = 1;
locklangevinspin[count2] = (FixLangevinSpin *) modify->fix[iforce];
count2++;
}
}
}
if (count2 != nlangspin)
error->all(FLERR,"Incorrect number of fix precession/spin");
// ptrs FixSetForceSpin classes
for (iforce = 0; iforce < modify->nfix; iforce++) {
@ -471,17 +517,16 @@ void FixNVESpin::ComputeInteractionsSpin(int i)
// update magnetic precession interactions
if (precession_spin_flag) {
lockprecessionspin->compute_single_precession(i,spi,fmi);
for (int k = 0; k < nprecspin; k++) {
lockprecessionspin[k]->compute_single_precession(i,spi,fmi);
}
}
// update langevin damping and random force
if (maglangevin_flag) { // mag. langevin
if (tdamp_flag) { // transverse damping
locklangevinspin->add_tdamping(spi,fmi);
}
if (temp_flag) { // spin temperature
locklangevinspin->add_temperature(fmi);
for (int k = 0; k < nlangspin; k++) {
locklangevinspin[k]->compute_single_langevin(i,spi,fmi);
}
}
@ -496,7 +541,6 @@ void FixNVESpin::ComputeInteractionsSpin(int i)
fm[i][0] = fmi[0];
fm[i][1] = fmi[1];
fm[i][2] = fmi[2];
}
/* ----------------------------------------------------------------------

17
src/SPIN/fix_nve_spin.h
View File

@ -61,11 +61,20 @@ friend class PairSpin;
int tdamp_flag, temp_flag;
int setforce_spin_flag;
// pointers to magnetic fixes
// pointers to fix langevin/spin styles
class FixPrecessionSpin *lockprecessionspin;
class FixLangevinSpin *locklangevinspin;
class FixSetForceSpin *locksetforcespin;
int nlangspin;
class FixLangevinSpin **locklangevinspin;
// pointers to fix setforce/spin styles
int nsetspin;
class FixSetForceSpin *locksetforcespin; // to be done
// pointers to fix precession/spin styles
int nprecspin;
class FixPrecessionSpin **lockprecessionspin;
// pointers to magnetic pair styles

215
src/SPIN/fix_precession_spin.cpp
View File

@ -67,6 +67,9 @@ FixPrecessionSpin::FixPrecessionSpin(LAMMPS *lmp, int narg, char **arg) :
H_field = 0.0;
nhx = nhy = nhz = 0.0;
hx = hy = hz = 0.0;
stt_field = 0.0;
nsttx = nstty = nsttz = 0.0;
sttx = stty = sttz = 0.0;
Ka = 0.0;
nax = nay = naz = 0.0;
Kax = Kay = Kaz = 0.0;
@ -74,8 +77,11 @@ FixPrecessionSpin::FixPrecessionSpin(LAMMPS *lmp, int narg, char **arg) :
nc1x = nc1y = nc1z = 0.0;
nc2x = nc2y = nc2z = 0.0;
nc3x = nc3y = nc3z = 0.0;
K6 = 0.0;
n6x = n6y = n6z = 0.0;
m6x = m6y = m6z = 0.0;
zeeman_flag = aniso_flag = cubic_flag = 0;
zeeman_flag = stt_flag = aniso_flag = cubic_flag = hexaniso_flag = 0;
int iarg = 3;
while (iarg < narg) {
@ -87,6 +93,14 @@ FixPrecessionSpin::FixPrecessionSpin(LAMMPS *lmp, int narg, char **arg) :
nhy = utils::numeric(FLERR,arg[iarg+3],false,lmp);
nhz = utils::numeric(FLERR,arg[iarg+4],false,lmp);
iarg += 5;
} else if (strcmp(arg[iarg],"stt") == 0) {
if (iarg+4 > narg) error->all(FLERR,"Illegal fix precession/spin command");
stt_flag = 1;
stt_field = utils::numeric(FLERR,arg[iarg+1],false,lmp);
nsttx = utils::numeric(FLERR,arg[iarg+2],false,lmp);
nstty = utils::numeric(FLERR,arg[iarg+3],false,lmp);
nsttz = utils::numeric(FLERR,arg[iarg+4],false,lmp);
iarg += 5;
} else if (strcmp(arg[iarg],"anisotropy") == 0) {
if (iarg+4 > narg) error->all(FLERR,"Illegal fix precession/spin command");
aniso_flag = 1;
@ -110,41 +124,111 @@ FixPrecessionSpin::FixPrecessionSpin(LAMMPS *lmp, int narg, char **arg) :
nc3y = utils::numeric(FLERR,arg[iarg+10],false,lmp);
nc3z = utils::numeric(FLERR,arg[iarg+11],false,lmp);
iarg += 12;
} else if (strcmp(arg[iarg],"hexaniso") == 0) {
if (iarg+7 > narg) error->all(FLERR,"Illegal fix precession/spin command");
hexaniso_flag = 1;
K6 = utils::numeric(FLERR,arg[iarg+1],false,lmp);
n6x = utils::numeric(FLERR,arg[iarg+2],false,lmp);
n6y = utils::numeric(FLERR,arg[iarg+3],false,lmp);
n6z = utils::numeric(FLERR,arg[iarg+4],false,lmp);
m6x = utils::numeric(FLERR,arg[iarg+5],false,lmp);
m6y = utils::numeric(FLERR,arg[iarg+6],false,lmp);
m6z = utils::numeric(FLERR,arg[iarg+7],false,lmp);
iarg += 8;
} else error->all(FLERR,"Illegal precession/spin command");
}
// normalize vectors
double inorm;
double norm2,inorm;
if (zeeman_flag) {
inorm = 1.0/sqrt(nhx*nhx + nhy*nhy + nhz*nhz);
norm2 = nhx*nhx + nhy*nhy + nhz*nhz;
if (norm2 == 0.0)
error->all(FLERR,"Illegal precession/spin command");
inorm = 1.0/sqrt(norm2);
nhx *= inorm;
nhy *= inorm;
nhz *= inorm;
}
if (stt_flag) {
norm2 = nsttx*nsttx + nstty*nstty + nsttz*nsttz;
if (norm2 == 0.0)
error->all(FLERR,"Illegal precession/spin command");
inorm = 1.0/sqrt(norm2);
nsttx *= inorm;
nstty *= inorm;
nsttz *= inorm;
}
if (aniso_flag) {
inorm = 1.0/sqrt(nax*nax + nay*nay + naz*naz);
norm2 = nax*nax + nay*nay + naz*naz;
if (norm2 == 0.0)
error->all(FLERR,"Illegal precession/spin command");
inorm = 1.0/sqrt(norm2);
nax *= inorm;
nay *= inorm;
naz *= inorm;
}
if (cubic_flag) {
inorm = 1.0/sqrt(nc1x*nc1x + nc1y*nc1y + nc1z*nc1z);
norm2 = nc1x*nc1x + nc1y*nc1y + nc1z*nc1z;
if (norm2 == 0.0)
error->all(FLERR,"Illegal precession/spin command");
inorm = 1.0/sqrt(norm2);
nc1x *= inorm;
nc1y *= inorm;
nc1z *= inorm;
inorm = 1.0/sqrt(nc2x*nc2x + nc2y*nc2y + nc2z*nc2z);
norm2 = nc2x*nc2x + nc2y*nc2y + nc2z*nc2z;
if (norm2 == 0.0)
error->all(FLERR,"Illegal precession/spin command");
inorm = 1.0/sqrt(norm2);
nc2x *= inorm;
nc2y *= inorm;
nc2z *= inorm;
inorm = 1.0/sqrt(nc3x*nc3x + nc3y*nc3y + nc3z*nc3z);
norm2 = nc3x*nc3x + nc3y*nc3y + nc3z*nc3z;
if (norm2 == 0.0)
error->all(FLERR,"Illegal precession/spin command");
inorm = 1.0/sqrt(norm2);
nc3x *= inorm;
nc3y *= inorm;
nc3z *= inorm;
}
if (hexaniso_flag) {
norm2 = n6x*n6x + n6y*n6y + n6z*n6z;
if (norm2 == 0.0)
error->all(FLERR,"Illegal precession/spin command");
inorm = 1.0/sqrt(norm2);
n6x *= inorm;
n6y *= inorm;
n6z *= inorm;
norm2 = m6x*m6x + m6y*m6y + m6z*m6z;
if (norm2 == 0.0)
error->all(FLERR,"Illegal precession/spin command");
inorm = 1.0/sqrt(norm2);
m6x *= inorm;
m6y *= inorm;
m6z *= inorm;
l6x = (n6z*m6y-n6y*m6z);
l6y = (n6x*m6z-n6z*m6x);
l6z = (n6y*m6x-n6x*m6y);
norm2 = l6x*l6x + l6y*l6y + l6z*l6z;
if (norm2 == 0.0)
error->all(FLERR,"Illegal precession/spin command");
inorm = 1.0/sqrt(norm2);
l6x *= inorm;
l6y *= inorm;
l6z *= inorm;
m6x = (l6z*n6y-l6y*n6z);
m6y = (l6x*n6z-l6z*n6x);
m6z = (l6y*n6x-l6x*n6y);
}
degree2rad = MY_PI/180.0;
time_origin = update->ntimestep;
@ -185,6 +269,7 @@ void FixPrecessionSpin::init()
Kah = Ka/hbar;
k1ch = k1c/hbar;
k2ch = k2c/hbar;
K6h = K6/hbar;
if (utils::strmatch(update->integrate_style,"^respa")) {
ilevel_respa = ((Respa *) update->integrate)->nlevels-1;
@ -199,15 +284,6 @@ void FixPrecessionSpin::init()
error->all(FLERR,"Illegal precession/spin command");
}
// check that fix precession/spin is only declared once
int iprec = 0;
for (int iforce = 0; iforce < modify->nfix; iforce++)
if (strstr(modify->fix[iforce]->style,"precession/spin")) iprec++;
if (iprec > 1)
error->all(FLERR,"precession/spin command can only be declared once");
varflag = CONSTANT;
if (magfieldstyle != CONSTANT) varflag = EQUAL;
@ -283,6 +359,11 @@ void FixPrecessionSpin::post_force(int /* vflag */)
epreci -= compute_zeeman_energy(spi);
}
if (stt_flag) { // compute Spin Transfer Torque
compute_stt(spi,fmi);
epreci -= compute_stt_energy(spi);
}
if (aniso_flag) { // compute magnetic anisotropy
compute_anisotropy(spi,fmi);
epreci -= compute_anisotropy_energy(spi);
@ -293,6 +374,11 @@ void FixPrecessionSpin::post_force(int /* vflag */)
epreci -= compute_cubic_energy(spi);
}
if (hexaniso_flag) { // compute hexagonal anisotropy
compute_hexaniso(spi,fmi);
epreci -= compute_hexaniso_energy(spi);
}
emag[i] += epreci;
eprec += epreci;
fm[i][0] += fmi[0];
@ -309,12 +395,16 @@ void FixPrecessionSpin::compute_single_precession(int i, double spi[3], double f
int *mask = atom->mask;
if (mask[i] & groupbit) {
if (zeeman_flag) compute_zeeman(i,fmi);
if (stt_flag) compute_stt(spi,fmi);
if (aniso_flag) compute_anisotropy(spi,fmi);
if (cubic_flag) compute_cubic(spi,fmi);
if (hexaniso_flag) compute_hexaniso(spi,fmi);
}
}
/* ---------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
Zeeman
------------------------------------------------------------------------- */
void FixPrecessionSpin::compute_zeeman(int i, double fmi[3])
{
@ -334,8 +424,32 @@ double FixPrecessionSpin::compute_zeeman_energy(double spi[4])
return energy;
}
/* ----------------------------------------------------------------------
STT
------------------------------------------------------------------------- */
void FixPrecessionSpin::compute_stt(double spi[3], double fmi[3])
{
double sx = spi[0];
double sy = spi[1];
double sz = spi[2];
fmi[0] += 1.0*stt_field*( sy*nsttz-sz*nstty);
fmi[1] += 1.0*stt_field*(-sx*nsttz+sz*nsttx);
fmi[2] += 1.0*stt_field*( sx*nstty-sy*nsttx);
}
/* ---------------------------------------------------------------------- */
double FixPrecessionSpin::compute_stt_energy(double spi[3])
{
double energy = 0.0; // Non-conservative force
return energy;
}
/* ----------------------------------------------------------------------
compute uniaxial anisotropy interaction for spin i
------------------------------------------------------------------------- */
void FixPrecessionSpin::compute_anisotropy(double spi[3], double fmi[3])
{
double scalar = nax*spi[0] + nay*spi[1] + naz*spi[2];
@ -393,9 +507,7 @@ void FixPrecessionSpin::compute_cubic(double spi[3], double fmi[3])
fmi[2] += (fourz + sixz);
}
/* ----------------------------------------------------------------------
compute cubic aniso energy of spin i
------------------------------------------------------------------------- */
/* ---------------------------------------------------------------------- */
double FixPrecessionSpin::compute_cubic_energy(double spi[3])
{
@ -412,6 +524,62 @@ double FixPrecessionSpin::compute_cubic_energy(double spi[3])
return energy;
}
/* ----------------------------------------------------------------------
compute hexagonal anisotropy interaction for spin i
------------------------------------------------------------------------- */
void FixPrecessionSpin::compute_hexaniso(double spi[3], double fmi[3])
{
double s_x,s_y,s_z;
double pf, phi, ssint2;
// changing to the axes' frame
s_x = l6x*spi[0]+l6y*spi[1]+l6z*spi[2];
s_y = m6x*spi[0]+m6y*spi[1]+m6z*spi[2];
s_z = n6x*spi[0]+n6y*spi[1]+n6z*spi[2];
// hexagonal anisotropy in the axes' frame
phi = atan2(s_y,s_x);
ssint2 = s_x*s_x + s_y*s_y; // s^2sin^2(theta)
pf = 6.0 * K6h * ssint2*ssint2*sqrt(ssint2); // 6*K_6*s^5*sin^5(theta)
double fm_x = pf*cos(5*phi);
double fm_y = -pf*sin(5*phi);
double fm_z = 0;
// back to the lab's frame
fmi[0] += fm_x*l6x+fm_y*m6x+fm_z*n6x;
fmi[1] += fm_x*l6y+fm_y*m6y+fm_z*n6y;
fmi[2] += fm_x*l6z+fm_y*m6z+fm_z*n6z;
}
/* ----------------------------------------------------------------------
compute hexagonal aniso energy of spin i
------------------------------------------------------------------------- */
double FixPrecessionSpin::compute_hexaniso_energy(double spi[3])
{
double energy = 0.0;
double s_x,s_y,s_z, phi,ssint2;
// changing to the axes' frame
s_x = l6x*spi[0]+l6y*spi[1]+l6z*spi[2];
s_y = m6x*spi[0]+m6y*spi[1]+m6z*spi[2];
s_z = n6x*spi[0]+n6y*spi[1]+n6z*spi[2];
// hexagonal anisotropy in the axes' frame
phi = atan2(s_y,s_z);
ssint2 = s_x*s_x + s_y*s_y;
energy = K6 * ssint2*ssint2*ssint2*cos(6*phi);
return 2.0*energy;
}
/* ---------------------------------------------------------------------- */
void FixPrecessionSpin::set_magneticprecession()
@ -421,6 +589,13 @@ void FixPrecessionSpin::set_magneticprecession()
hy = H_field*nhy;
hz = H_field*nhz;
}
if (stt_flag) {
sttx = stt_field*nsttx;
stty = stt_field*nstty;
sttz = stt_field*nsttz;
}
if (aniso_flag) {
Kax = 2.0*Kah*nax;
Kay = 2.0*Kah*nay;

25
src/SPIN/fix_precession_spin.h
View File

@ -39,7 +39,7 @@ class FixPrecessionSpin : public Fix {
void min_post_force(int);
double compute_scalar();
int zeeman_flag, aniso_flag, cubic_flag;
int zeeman_flag, stt_flag, aniso_flag, cubic_flag, hexaniso_flag;
void compute_single_precession(int, double *, double *);
// zeeman calculations
@ -47,6 +47,11 @@ class FixPrecessionSpin : public Fix {
void compute_zeeman(int, double *);
double compute_zeeman_energy(double *);
// stt calculations
void compute_stt(double *, double *);
double compute_stt_energy(double *);
// uniaxial aniso calculations
void compute_anisotropy(double *, double *);
@ -57,6 +62,11 @@ class FixPrecessionSpin : public Fix {
void compute_cubic(double *, double *);
double compute_cubic_energy(double *);
// hexagonal aniso calculations
void compute_hexaniso(double *, double *);
double compute_hexaniso_energy(double *);
// storing magnetic energies
int nlocal_max; // max nlocal (for list size)
@ -83,6 +93,12 @@ class FixPrecessionSpin : public Fix {
double nhx, nhy, nhz;
double hx, hy, hz; // temp. force variables
// STT intensity and direction
double stt_field;
double nsttx, nstty, nsttz;
double sttx, stty, sttz;
// magnetic anisotropy intensity and direction
double Ka; // aniso const. in eV
@ -98,6 +114,13 @@ class FixPrecessionSpin : public Fix {
double nc2x,nc2y,nc2z;
double nc3x,nc3y,nc3z;
// hexagonal anisotropy
double K6; // hexagonal aniso const. in eV
double K6h; // hexagonal aniso const. in rad.THz
double n6x,n6y,n6z; // main axis
double m6x,m6y,m6z; // secondary (perpendicular) axis
double l6x,l6y,l6z; // =(m x n)
void set_magneticprecession();
};