Hengjia Wang
Clemson University
hengjiw at g.clemson.edu

Calculations of lattice vibrational mode lifetimes using Jazz: a new Python wrapper for LAMMPS

Jazz is a new Python wrapper for LAMMPS, implemented to calculate the lifetimes of vibrational normal modes. It is now included in the third-party contributions to LAMMPS and is available freely to the community.

The new approach is based on the novel combination of two modern techniques: Liouvillian operator and the recursion method. Calculations of mode lifetimes using this new approach are much faster than previous methods because they are based on phase-space integrals, which can be done by standard Monte Carlo techniques. Other advantages of Jazz include that it has fewer limitations than other methods.

Using Python as the interface, Jazz treats LAMMPS as a blackbox source of energies and forces and manages the Metropolis Mento Carlo process, displacing the atoms in a controlled way, querying LAMMPS for energies to make the accept/reject decision. The force extracted from LAMMPS and the appropriate averages obtained form the moment-based approximation to the vibrational lifetime of each mode.

There are three primary python modules in the package:

1 - genvecs0 (determines normal modes from dynamical matrix) 2 - calcavgs (does the Monte Carlo averaging) 3 - calcmoments ( combines the Mon Carlo averaging to calculate moments and lifetimes)

The theory, background, along with the implementation of Jazz (with examples), will be covered.