117 lines
3.7 KiB
Plaintext
117 lines
3.7 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Commands_all.html)
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:line
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fix precession/spin command :h3
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[Syntax:]
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fix ID group precession/spin style args :pre
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ID, group are documented in "fix"_fix.html command :ulb,l
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precession/spin = style name of this fix command :l
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style = {zeeman} or {anisotropy} or {cubic} :l
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{zeeman} args = H x y z
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H = intensity of the magnetic field (in Tesla)
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x y z = vector direction of the field
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{anisotropy} args = K x y z
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K = intensity of the magnetic anisotropy (in eV)
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x y z = vector direction of the anisotropy :pre
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{cubic} args = K1 K2c n1x n1y n1x n2x n2y n2z n3x n3y n3z
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K1 and K2c = intensity of the magnetic anisotropy (in eV)
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n1x to n3z = three direction vectors of the cubic anisotropy :pre
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:ule
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[Examples:]
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fix 1 all precession/spin zeeman 0.1 0.0 0.0 1.0
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fix 1 3 precession/spin anisotropy 0.001 0.0 0.0 1.0
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fix 1 iron precession/spin cubic 0.001 0.0005 1.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 1.0
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fix 1 all precession/spin zeeman 0.1 0.0 0.0 1.0 anisotropy 0.001 0.0 0.0 1.0 :pre
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[Description:]
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This fix applies a precession torque to each magnetic spin in the group.
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Style {zeeman} is used for the simulation of the interaction
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between the magnetic spins in the defined group and an external
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magnetic field:
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:c,image(Eqs/force_spin_zeeman.jpg)
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with mu0 the vacuum permeability, muB the Bohr magneton (muB = 5.788 eV/T
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in metal units).
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Style {anisotropy} is used to simulate an easy axis or an easy plane
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for the magnetic spins in the defined group:
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:c,image(Eqs/force_spin_aniso.jpg)
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with n defining the direction of the anisotropy, and K (in eV) its intensity.
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If K>0, an easy axis is defined, and if K<0, an easy plane is defined.
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Style {cubic} is used to simulate a cubic anisotropy, with three
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possible easy axis for the magnetic spins in the defined group:
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:c,image(Eqs/fix_spin_cubic.jpg)
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with K1 and K2c (in eV) the intensity coefficients and
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n1, n2 and n3 defining the three anisotropic directions
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defined by the command (from n1x to n3z).
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For n1 = (100), n2 = (010), and n3 = (001), K1 < 0 defines an
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iron type anisotropy (easy axis along the (001)-type cube
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edges), and K1 > 0 defines a nickel type anisotropy (easy axis
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along the (111)-type cube diagonals).
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K2^c > 0 also defines easy axis along the (111)-type cube
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diagonals.
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See chapter 2 of "(Skomski)"_#Skomski1 for more details on cubic
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anisotropies.
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In all cases, the choice of (x y z) only imposes the vector
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directions for the forces. Only the direction of the vector is
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important; it's length is ignored (the entered vectors are
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normalized).
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Those styles can be combined within one single command line.
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:line
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[Restart, fix_modify, output, run start/stop, minimize info:]
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By default, the energy associated to this fix is not added to the potential
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energy of the system.
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The "fix_modify"_fix_modify.html {energy} option is supported by this fix
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to add this magnetic potential energy to the potential energy of the system,
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fix 1 all precession/spin zeeman 1.0 0.0 0.0 1.0
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fix_modify 1 energy yes :pre
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This fix computes a global scalar which can be accessed by various
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"output commands"_Howto_output.html.
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No information about this fix is written to "binary restart
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files"_restart.html.
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[Restrictions:]
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The {precession/spin} style is part of the SPIN package. This style
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is only enabled if LAMMPS was built with this package, and if the
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atom_style "spin" was declared. See the "Build
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package"_Build_package.html doc page for more info.
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[Related commands:]
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"atom_style spin"_atom_style.html
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[Default:] none
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:line
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:link(Skomski1)
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[(Skomski)] Skomski, R. (2008). Simple models of magnetism.
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Oxford University Press.
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