How to handle pseudopotentials ?

[David Waroquiers]

This issue concerns how to handle pseudopotentials.

There are probably two things there. The first one is how are they handled at the python level. The other one is how the actual abinit input file is written.

For the abinit input file, we have decided with @gmrigna that we won't support the versions of abinit before 9.2 and only support running abinit without the .files file (see B.7 in the release notes of abinit v9.2 : https://docs.abinit.org/about/release-notes/). That means that the pseudos will be handled with the pseudos variable (https://docs.abinit.org/variables/files/#pseudos), possibly together with the pp_dirpath.

At the python level, we have different options. For pseudos from the pseudo-dojo, we could use a string identifier corresponding to a specific PD table/xc/version etc ... for a given atom. This will need a few changes in the pseudo_dojo package as well but it is worth it (there are some drawbacks with the current situation but I will not get into details here). We also need to allow for custom pseudos.