Projected band structure issues

[utf]

Projected band structures currently have the following issues:

• Cryptic error messages when the projection string is not exactly as expected (e.g. incorrect number of projections, elements/orbitals don't exist, projections don't exist).
• RGB mode only supports 3 orbitals (not 2 or 1).

[ajjackson]

To which I will add from #32

@cnsavory commented on 13 May

Something coming up from the Questaal workshop - sumo currently isn't able to plot Questaal derived band structures separated by orbital contribution, as it can for VASP. The fplot implementation involves a separate run for the selected orbital but still outputs one bnds file, so hopefully wouldn't change the sumo workflow too much. Could band projection for Questaal band structures be a possible option for a future sumo release?

@ajjackson commented on 13 May

If there's a sensible workflow to get the information out, it shouldn't be too hard to "do it like vasp". I think we can improve the final appearance from Vasp too, but that part should be shared in any case.

Do we have a consistent recipe for getting a known set of useful information? As with the DOS plotter, I'd rather we keep the sumo settings simple, generate a lot of data and deal with summing etc in sumo if need be. I'm a little worried by the prospect of multiple Questaal runs, do you have to rename any files to avoid clobbering?

Is this issue suitable to discuss orbital projection plans in general, including support for other codes?

[utf]

As the orbital project band structure plots seem to be the most used feature of sumo, I'm happy to have a thread dedicated to them.

Based on feedback from some users in Ram's group, I think future versions should try and support:

• Custom colors in rgb mode for accessibility and aesthetic reasons. E.g., can we define a triangle on the colour wheel and interpolate between the colours at the vertices.
• Better support for projected spin polarized band structures. E.g. can we make a custom dashed rgb line (and also something similar for other projection modes), that can represent spin up and spin down bands differently. Ram's group were using a custom version of sumo with mode=stacked, in which the spin down bands were interpolated a much coarser grid, making it appear dashed. It would be nice to support this properly.

Personally, I'd also like to support spin projected band structures for spin-orbit coupling calculations (fplot in questaal can already do this). The spin contributions (for the x, y, and z directions defined relative to SAXIS) are already given in the vasprun.xml but are not parsed correctly by pymatgen, so I don't think this will be too much extra work.

[ajjackson]

I guess the ideal approach would be to make sure the data structures and VASP importer are fully-featured on the pymatgen side, then we can add more plotting modes and other code importers on the Sumo side.

[muhammadaliaskari]

Is it possible to plot band structure of a composite with more than 3 different elements because --mode stacked option does not work for my structure?

[utf]

An update on this: I just added parsing of the projected magnetisation from SOC calculations to pymatgen (materialsproject/pymatgen#2065), so spin projected band structures could be added to sumo relatively easily.