Bands

[WuyihanVictor]

• Support compute_bands for an explicit kpath, and save results to compute_bands.json
• Check for SCF convergence before running POSTSCF. If SCF is not converged, POSTSCF will not run
• Support SCF maxtime. If not specified, maxtime = Year(1)

[mfherbst]

Thanks, I cleaned up the maxtime code a bit in #14. For the kpoints / bands I have no idea how to do that properly as I know too little about the python side.

I think the basic idea you propose is reasonable, but it might also be nice to be able to just run the computation without explicitly specifying the path. What I'm thinking is to just run supply a kline_density and let DFTK figure out the kpath by itself, for example. But in line with the above, not sure to what extend this makes sense.

My intuition is to work with an interpolation syntax like $ExplicitKpoints again, just to reserve the right to generalise to other things later.