Quesadilla

Quesadilla (Queue-saving nondiagonal superlattices) is a python package for nondiagonal supercell phonon calculations, using the approach of Lloyd-Williams and Monserrat

Features

• A simple, phonopy-like interface for generating NDSCs and computing force constants.
• Supports all force calculators supported by phonopy (VASP, QE, Wien2k, etc.).
• Generates standard phonopy.yaml files that can be used with phonopy or any other package that reads phonopy output files.
• Heavily uses symmetry to minimize the computational cost of the calculations.
• Solves the set cover problem to extract the minimum number of NDSCs needed to cover the irreducible part of the $q$-grid.

Installation

Quesadilla requires a FORTRAN compiler and a BLAS/LAPACK installation on your path. It has only been tested on Linux and MacOS. The package is not yet listed on PyPI, so you need to install it directly from the GitHub repository via pip:

pip install [email protected]:Griffin-Group/quesadilla.git

If you have any issues with the installation, please open an issue.

Usage

Quesadilla has a simple CLI that is nearly identical to phonopy. If you know how to use phonopy, you already know how to use Quesadilla! See the full tutorial for more details.

To generate the NDSCs, you can run

quesadilla -d --dim 4 4 4

which will find the smallest number of NDSCs that cover the irreducible part of a 4x4x4 $q$-grid. You can then use your favorite force calculator to compute the forces in these supercells, and then run

quesadilla -f vasprun.xml

to create the FORCE_SETS file for each NDSC. Finally, you can compute the force constants in the full 4x4x4 supercell by running

quesadilla --fc

which will produce a phonopy.yaml file that can be used with phonopy or any other package that reads phonopy output files.