Phonopy calculations with FHIvibes

Disclaimer

FHIvibes is not yet released and in beta stage, e.g., the software still has its old name hilde. Sorry for any inconvenience.

Learning objectives

In this tutorial you will learn how to

1) use FHIvibes to perform basic lattice dynamics investigations within the harmonic approximation using the finitie differences approach as implemented in phonopy, 2) analyze data obtained from ab initio molecular dynamics simulations via FHIvibes and feed it to hiphive to obtain phonon dispersions.

Prerequisites

FHIvibes is not yet released, so we provide a virtual environment holding the necessary software for part 1 via

• virtualbox 6.0 or compatible.

For part 2, there are no special requirements other than a working python3 environment.

Part 1

The main tutorial comprises two parts that cover the basics of performing ab initio lattice dynamics investigations in the harmonic approximation via phonopy, which is one aspect of the integrated framework FHIvibes. FHIvibes comes with a command line interface for setting up and performing ab initio calculations via FHIaims, and analyzing the results.

Performing phonopy calculations

• basics of phonon calculations with the finite difference method as implemented in phonopy
• using the quasi harmonic approximation to estimate lattice expansion.

Electron-Phonon Coupling: Band Gap Renormalization

• influence of lattice expansion on the electronic band gap
• influence of atomic motion on electronic band gap

Part 2

FHIvibes also features ab initio molecular dynamics calculations that cannot be covered in this tutorial. However, I provide simulation data from such a simulation in the form of an xarray dataset here. I provide two jupyter notebooks, one for inspecting the dataset and playing around with the data, another for extracting force constants via hiphive which, e.g., allows to plot a phonon dispersion.