[WIP] Implementation of quasi-harmonic approximation

[JaGeo]

Summary

One way to compute thermodynamic properties of materials is by using the quasi-harmonic approximation. This is an attempt to implement this qha based on the EOS Maker and the harmonic phonon runs.

Closes #890

[JaGeo]

@esoteric-ephemera I am adding you as a collaborator to my repo so that you can contribute at a later stage, if you would like to. I would be especially happy about feedback on the EOS - phonon connection. I will try to reuse us much code from the normal EOS fits as possible.

[JaGeo]

@esoteric-ephemera Never mind. I think I realized how to use the class correctly without using the make functionality ;). Sorry about this!

[JaGeo]

@esoteric-ephemera I think I will also directly use the phonopy api (https://github.com/phonopy/phonopy/blob/develop/phonopy/api_qha.py) to avoid redundant reimplementations. However, this will make different eos available for the qha than in the normal eos fit.

@utf do you think this would be an issue?

[JaGeo]

ToDo:

• Reduce number of steps in the workflow
• Finalize Force field tests
• Check all units and add field descriptions
• Document the workflows
• Fix all linting issues
• write workflows for the different force fields
• add a VASP Workflow (with minimal settings)

[JaGeo]

I am closing this and reopen. Something seems to be messed up with the tests.