pair_style spin/exchange command

Syntax

pair_style spin/exchange cutoff
  • cutoff = global cutoff pair (distance in metal units)

Examples

pair_style spin/exchange 4.0
pair_coeff * * exchange 4.0 0.0446928 0.003496 1.4885
pair_coeff 1 2 exchange 6.0 -0.01575 0.0 1.965

Description

Style spin/exchange computes the exchange interaction between pairs of magnetic spins:

_images/pair_spin_exchange_interaction.jpg

where si and sj are two neighboring magnetic spins of two particles, rij = ri - rj is the inter-atomic distance between the two particles, and J(rij) is a function defining the intensity and the sign of the exchange interaction.

This function is defined as:

_images/pair_spin_exchange_function.jpg

where a, b and d are the three constant coefficients defined in the associated “pair_coeff” command.

The coefficients a, b, and d need to be fitted so that the function above matches with the value of the exchange interaction for the N neighbor shells taken into account.

Examples and more explanations about this function and its parametrization are reported in (Tranchida).

From this exchange interaction, each spin i will be submitted to a magnetic torque omega, and its associated atom can be submitted to a force F for spin-lattice calculations (see fix_nve_spin), such as:

_images/pair_spin_exchange_forces.jpg

with h the Planck constant (in metal units).

More details about the derivation of these torques/forces are reported in (Tranchida).


Restrictions

All the pair/spin styles are part of the SPIN package. These styles are only enabled if LAMMPS was built with this package, and if the atom_style “spin” was declared. See the Making LAMMPS section for more info.