Commit JT 111519

This directory contains examples and applications of the SPIN package

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- the benchmark directory provides comparison between LAMMPS

  results and a series of simple test problems (coded as python

  scripts).

- the iron, cobalt_hcp, cobalt_fcc and nickel directories provide 

  examples of spin-lattice calculations.

** Note, the aim of this repository is mainly to provide users with

examples. Better values and tuning of the magnetic and mechanical 

interactions can be achieved for more accurate materials 

interactions can (have to...) be achieved for more accurate materials 

simulations. **

** The objective of the benchmark examples in this directory 

   is the following twofold: 

- verify the implementation of the LAMMPS' SPIN package by 

  comparing its results to well-known analytic results, or 

  to simple test problems,

- provide users with simple comparisons, allowing them to 

  better understand what is implemented in the code.

The LAMMPS input file (bench-*) can be modified, as well as the

associated python script, in order to try different comparisons.

All scripts can be run by executing the shell script from its

directory. Example:

./run-bench-exchange.sh from the benchmarck_damped_exchange/

directory. 

** Below a brief description of the different benchmark 

   problems:

- benchmarck_damped_precession:

  simulates the damped precession of a single spin in a magnetic

  field. 

  Run as: ./run-bench-prec.sh

  Output: x, y and z components of the magnetization, and

  magnetic energy.

- benchmarck_damped_exchange:

  simulates two spins interacting through the exchange

  interaction. The parameters in the LAMMPS input script

  (bench-spin-precession.in) are calibrated to match the

  exchange definition in the python script (llg_exchange.py). 

  Run as: ./run-bench-exchange.sh

  Output: average magnetization resulting from the damped 

  precession of the two interacting spins. Also plots the 

  evolution of the magnetic energy.

- benchmarck_langevin_precession:

  simulates a single spin in a magnetic field and in contact

  with a thermal bath, and compares the statistical averages of 

  the output to the analytical result of the Langevin function. 

  Run as: ./run-bench-prec.sh

  Output: statistical average of the z-component of the

  magnetization (along the applied field) and of the magnetic

  energy versus temperature. Comparison to the Langevin function

  results (computed by the python script).

  Note: This example is a reworked version of a test problem 

  provided by Martin Kroger (ETHZ).  

mass            1 1.0

set             type 1 spin 2.0 1.0 0.0 0.0

# defines a pair/style for neighbor list, but do not use it

pair_style      spin/exchange 4.0

pair_coeff      * * exchange 1.0 0.0 0.0 1.0

variable        H equal 10.0

variable        Kan equal 0.0

variable        Temperature equal 0.0 

variable        RUN equal 100000

variable        Nsteps equal 500000

fix             1 all nve/spin lattice no

fix             2 all precession/spin zeeman ${H} 0.0 0.0 1.0 anisotropy ${Kan} 0.0 0.0 1.0

timestep	0.0001

run             ${RUN}

run             ${Nsteps}