# Phonopy calculations with FHIvibes

**Florian Knoop**

## 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.