Commit JT 032519

min_modify keyword values ... :pre

one or more keyword/value pairs may be listed :ulb,l

keyword = {dmax} or {line}

keyword = {dmax} or {line} or {alpha_damp} or {discret_factor}

  {dmax} value = max

    max = maximum distance for line search to move (distance units)

  {line} value = {backtrack} or {quadratic} or {forcezero}

    backtrack,quadratic,forcezero = style of linesearch to use :pre

    backtrack,quadratic,forcezero = style of linesearch to use 

  {alpha_damp} value = damping

    damping = fictitious Gilbert damping for spin minimization (adim)

  {discret_factor} value = factor

    factor = discretization factor for adaptive spin timestep (adim) :pre

:ule

[Examples:]

that difference may be smaller than machine epsilon even if atoms

could move in the gradient direction to reduce forces further.

Keywords {alpha_damp} and {discret_factor} only make sense when

a "min_spin"_min_spin.html command is declared. 

Keyword {alpha_damp} defines an analog of a magnetic Gilbert

damping. It defines a relaxation rate toward an equilibrium for

a given magnetic system. 

Keyword {discret_factor} defines a discretization factor for the

adaptive timestep used in the {spin} minimization. 

See "min_spin"_min_spin.html for more information about those

quantities. 

Default values are alpha_damp = 1.0 and discret_factor = 10.0.

[Restrictions:] none

[Related commands:]

"LAMMPS WWW Page"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)

:link(ld,Manual.html)

:link(lc,Commands_all.html)

:line

min_style spin command :h3

[Syntax:]

min_style spin :pre

[Examples:]

min_style 	spin

min_modify      alpha_damp 1.0 discret_factor 10.0 :pre

[Description:]

Apply a minimization algorithm to use when a "minimize"_minimize.html

command is performed.

Style {spin} defines a damped spin dynamics with an adaptive

timestep, according to:

:c,image(Eqs/min_spin_damping.jpg)

with lambda a damping coefficient (similar to a Gilbert damping)

Lambda can be defined by setting the {alpha_damp} keyword with the 

"min_modify"_min_modify.html command. 

The minimization procedure solves this equation using an

adaptive timestep. The value of this timestep is conditionned 

by the largest precession frequency that has to be solved in the 

system:

:c,image(Eqs/min_spin_timestep.jpg)

with |omega|_{max} the norm of the largest precession frequency

in the system (across all processes, and across all replicas if a

spin/neb calculation is performed). 

Kappa defines a discretization factor {discret_factor} for the 

definition of this timestep. 

{discret_factor} can be defined with the "min_modify"_min_modify.html

command.

NOTE: The {spin} style replaces the force tolerance by a torque

tolerance. See "minimize"_minimize.html for more explanation. 

[Restrictions:] none

[Related commands:]

"min_style"_min_style.html, "minimize"_minimize.html, 

"min_modify"_min_modify.html

[Default:]

The option defaults are alpha_damp = 1.0 and discret_factor =

10.0.

min_style style :pre

style = {cg} or {hftn} or {sd} or {quickmin} or {fire} :ul

style = {cg} or {hftn} or {sd} or {quickmin} or {fire} or {spin} :ul

[Examples:]

min_style cg

min_style spin

min_style fire :pre

[Description:]

of each atom is initialized to 0.0 by this style, at the beginning of

a minimization.

Style {spin} is a damped spin dynamics with an adaptive 

timestep.

See the "min/spin"_min_spin.html doc page for more information.

Either the {quickmin} and {fire} styles are useful in the context of

nudged elastic band (NEB) calculations via the "neb"_neb.html command.

the number of outer iterations or timesteps exceeds {maxiter}

the number of total force evaluations exceeds {maxeval} :ul

NOTE: the "minimization style"_min_style.html {spin} replaces

the force tolerance {ftol} by a torque tolerance.

The minimization procedure stops if the 2-norm (length) of the 

global torque vector (defined as the cross product between the 

spins and their precession vectors omega) is less than {ftol}, 

or if any of the other criteria are met.

NOTE: You can also use the "fix halt"_fix_halt.html command to specify

a general criterion for exiting a minimization, that is a calculation

performed on the state of the current system, as defined by an

# bfo in a 3d periodic box

units 		metal

dimension 	3

boundary 	p p f

atom_style 	spin

# necessary for the serial algorithm (sametag)

atom_modify 	map array 

lattice 	sc 3.96

region 		box block 0.0 34.0 0.0 34.0 0.0 1.0

create_box 	1 box

create_atoms 	1 box

# setting mass, mag. moments, and interactions for bcc iron

mass		1 1.0

set 		group all spin/random 11 2.50

pair_style 	hybrid/overlay spin/exchange 6.0 spin/magelec 4.5 spin/dmi 4.5

pair_coeff 	* * spin/exchange exchange 6.0 -0.01575 0.0 1.965

#pair_coeff 	* * spin/magelec magelec 4.5 0.000109 1.0 1.0 1.0

pair_coeff 	* * spin/magelec magelec 4.5 0.00109 1.0 1.0 1.0

pair_coeff 	* * spin/dmi dmi 4.5 0.00005 1.0 1.0 1.0

neighbor 	0.1 bin

neigh_modify 	every 10 check yes delay 20

#fix 		1 all precession/spin zeeman 0.001 0.0 0.0 1.0 anisotropy 0.01 1.0 0.0 0.0 

fix 		1 all precession/spin anisotropy 0.0000033 0.0 0.0 1.0

fix_modify	1 energy yes

fix 		2 all langevin/spin 0.0 0.1 21

fix		3 all nve/spin lattice no 

timestep	0.0001

compute 	out_mag    all spin

compute 	out_pe     all pe

compute 	out_ke     all ke

compute 	out_temp   all temp

variable 	magz      equal c_out_mag[3]

variable 	magnorm   equal c_out_mag[4]

variable 	emag      equal c_out_mag[5]

variable 	tmag      equal c_out_mag[6]

thermo          50

thermo_style    custom step time v_magnorm v_emag v_tmag temp etotal

thermo_modify   format float %20.15g

compute 	outsp all property/atom spx spy spz sp fmx fmy fmz

dump 		1 all custom 50 dump.lammpstrj type x y z c_outsp[1] c_outsp[2] c_outsp[3] c_outsp[4] c_outsp[5] c_outsp[6] c_outsp[7]

min_style	spin

min_modify 	alpha_damp 1.0 discret_factor 10.0

minimize        0.0 0.0 10000 1000