Implement features now available in DFTK

[mfherbst]

Things already available in AiidaDFTK, but not in here:

• The file "self_consistent_field.json" now contains all SCF information without ρ and ψ
• The JLD2 file referenced by "scf/checkpointfile" contains all data of the JSON, plus additionally ρ, but not ψ. It is used automatically to restart a calculation if it is present. Can be read using h5py.
• If "scf/save_ψ" is true, then this JLD2 file contains both ρ and ψ. It can be read using h5py from python.

Things which are available in DFTK and which we could easily make available here:

• Cancel SCF gracefully after timeout (see also Precompilation and maxtime flag epfl-matmat/AiidaDFTK.jl#14)
• Band structure calculation and dumping (see also Implement band structure calculation and bands dumping epfl-matmat/AiidaDFTK.jl#9)
  This includes computing eigenvalues and wave functions at arbitrary k-points.
  • Question is also a little how to best trigger this from Aiida (i.e. how to supply k-points or paths etc.), this will influence how Implement band structure calculation and bands dumping epfl-matmat/AiidaDFTK.jl#9 is implemented.
• Geometry optimisation via the geometry optimisation package (https://github.com/JuliaMolSim/GeometryOptimization.jl/)

[mfherbst]

Tagging @azadoks

[WuyihanVictor]

• "scf/save_ψ" is natively supported in aiida-dftk, since it is inside the "parameters" dict, and I have tested it.
• I have a draft implementaion of "maxtime" and "compute_bands" in my fork of AiidaDFTK https://github.com/WuyihanVictor/AiidaDFTK.jl/tree/bands. It takes in a explicit list of kpoints, which will be generated from the AiiDA side, and output a compute_bands.hdf5 containing the kpath, eigenvalues, and occupations.
• However, we need to decide whether to wirte a new DftkBandsWorkchain like in aiida-qe https://github.com/aiidateam/aiida-quantumespresso/blob/main/src/aiida_quantumespresso/workflows/pw/bands.py, or just put it into the base calculation.
• Thanks to the "maxtime", We can safely stop SCF when approaching the walltime. e.g., we can set maxtime=walltime-buffer_time_for_saving

[mfherbst]

I have a draft implementaion of "maxtime" and "compute_bands" in my fork of AiidaDFTK

Great, can you open a PR? Then we can discuss your open points there.

we need to decide whether to wirte a new DftkBandsWorkchain

No idea. I mean in principle once the SCF result has been written to disk, the band computation should be fast, so one could call AiidaDFTK a second time to kick that calculation off. @azadoks What you you think is better ?