In this exercise we are going to show how to obtain Phonon spectra using CP2K.

While some solid state code packages (like Quantum Espresso) contain functionality to calculate phonon spectra, CP2K does not. Using the Phonopy package it is nevertheless possible to calculate them using the Finite Displacement Method (FDM) with CP2K as the backend to calculate the forces.

Since the support for CP2K in Phonopy was added very recently and no new version of Phonopy was released yet, you have to install it in your home-directory on the server from a snapshot of the source code repository using the following command which will download the package and its requirements:

pip install --user https://github.com/atztogo/phonopy/archive/develop.zip

afterwards you will have the command phonopy available in ~/.local/bin. To make it known to the shell as any other command, run the following and logout and login back again:

echo 'export PATH="${HOME}/.local/bin:${PATH}"' >> .bashrc

Now you should be able to run phonopy –help as follows and get some help text:

studentXY@tcopt3 ~ $ phonopy --help
Usage: phonopy [options]

Options:
  -h, --help            show this help message and exit
[...]

Phonopy works in 3 stages:

1. It takes a CP2K input file containing at least a cell specification plus coordinates for a crystal and generates a number of input file skeletons containing new cell definitions and new coordinates
2. You have to take these input file skeletons, complete them with the rest of the simulation parameters and run a energy+forces simulation. The input file skeleton will also contain an option for CP2K to write the forces into a separate file
3. Phonopy is then run a second time to parse these forces and generate a so-called force set out of it
4. The third time Phonopy is called, it is used to actually calculate and generate a plot of the phonon band structure for a given path