109 lines
2.8 KiB
ReStructuredText
109 lines
2.8 KiB
ReStructuredText
.. index:: pair\_style spin/dmi
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pair\_style spin/dmi command
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============================
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Syntax
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""""""
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.. parsed-literal::
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pair_style spin/dmi cutoff
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* cutoff = global cutoff pair (distance in metal units)
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Examples
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""""""""
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.. parsed-literal::
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pair_style spin/dmi 4.0
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pair_coeff \* \* dmi 2.6 0.001 1.0 0.0 0.0
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pair_coeff 1 2 dmi 4.0 0.00109 0.0 0.0 1.0
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Description
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"""""""""""
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Style *spin/dmi* computes the Dzyaloshinskii-Moriya (DM) interaction
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between pairs of magnetic spins.
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According to the expression reported in :ref:`(Rohart) <Rohart>`, one has
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the following DM energy:
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.. image:: Eqs/pair_spin_dmi_interaction.jpg
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:align: center
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where si and sj are two neighboring magnetic spins of two particles,
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eij = (ri - rj)/\|ri-rj\| is the unit vector between sites i and j,
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and D is the DM vector defining the intensity (in eV) and the direction
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of the interaction.
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In :ref:`(Rohart) <Rohart>`, D is defined as the direction normal to the film oriented
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from the high spin-orbit layer to the magnetic ultra-thin film.
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The application of a spin-lattice Poisson bracket to this energy (as described
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in :ref:`(Tranchida) <Tranchida5>`) allows to derive a magnetic torque omega, and a
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mechanical force F (for spin-lattice calculations only) for each magnetic
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particle i:
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.. image:: Eqs/pair_spin_dmi_forces.jpg
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:align: center
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More details about the derivation of these torques/forces are reported in
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:ref:`(Tranchida) <Tranchida5>`.
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For the *spin/dmi* pair style, the following coefficients must be defined for
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each pair of atoms types via the :doc:`pair_coeff <pair_coeff>` command as in
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the examples above, or in the data file or restart files read by the
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:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>` commands, and
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set in the following order:
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* rc (distance units)
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* \|D\| (energy units)
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* Dx, Dy, Dz (direction of D)
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Note that rc is the radius cutoff of the considered DM interaction, \|D\| is
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the norm of the DM vector (in eV), and Dx, Dy and Dz define its direction.
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None of those coefficients is optional. If not specified, the *spin/dmi*
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pair style cannot be used.
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----------
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Restrictions
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""""""""""""
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All the *pair/spin* styles are part of the SPIN package. These styles
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are only enabled if LAMMPS was built with this package, and if the
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atom\_style "spin" was declared. See the :doc:`Build package <Build_package>` doc page for more info.
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Related commands
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""""""""""""""""
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:doc:`atom_style spin <atom_style>`, :doc:`pair_coeff <pair_coeff>`,
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:doc:`pair_eam <pair_eam>`,
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**Default:** none
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----------
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.. _Rohart:
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.. _Tranchida5:
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**(Rohart)** Rohart and Thiaville,
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Physical Review B, 88(18), 184422. (2013).
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**(Tranchida)** Tranchida, Plimpton, Thibaudeau and Thompson,
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Journal of Computational Physics, 372, 406-425, (2018).
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