Add pp_version flag to Vasp input sets

[Andrew-S-Rosen]

Closes #1692. Marked as draft until the next ASE release.

[Andrew-S-Rosen]

@zulissi Can you confirm what version pseudopotentials are used for OC? I didn't see it in the original OC paper.

[mshuaibii]

Thanks Andrew!

54 for OC

[Andrew-S-Rosen]

Thanks, @mshuaibii! Then this should be the only changes needed in the PR. You may want to bump the minimum ASE version when the next release comes out so users are guaranteed to be getting the right version of the pseudopotentials in their runs.

[mshuaibii]

Sounds good.

Do the upstream changes also allow you to just specify a directory here instead of "54"? I assume there's some assumption being made what the directory name should be. Sorry haven't had a chance to go through it yet!

[Andrew-S-Rosen]

Do the upstream changes also allow you to just specify a directory here instead of "54"? I assume there's some assumption being made what the directory name should be. Sorry haven't had a chance to go through it yet!

They actually always allowed you to do that with the pp flag. The way the pp_version flag works is that if you put all the VASP-provided pseudopotential folders in one parent directory (defined by the VASP_PP_PATH environment variable as usual), the Vasp calculator will automatically select the one based on your chosen xc (PBE or LDA) and pp_version. For instance, xc="PBE" and pp_version="54" select potpaw_PBE.54. None of that annoying symlinking stuff to potpaw or potpaw_PBE that ASE has historically required, although it does not break backwards compatibility if pp_version is not set.

[Andrew-S-Rosen]

Alright, the newest version of ASE is released and should work with these changes.