Findable electron density

We have received the request to add charge/electron density to the extracted data (from @nhoffmann and Santiago in the SOL group, to be included into the discussion). Concretely, this would require several sub-features, which will have their own use in the project at different progress steps:

• Quantify the amount of necessary raw files.
• Defining the data structure with the following constraints:
  • Storage efficiency: do we use a storage efficient representation (e.g. spherical harmonics) or maybe compression (@mscheidg how feasible do you think this is?).
  • Ease of working: the system should at least be ready as LibXC input. In general, a cube-like format with coordinates seems easy to manipulate.
  • Minimal/controlled information loss during transformation of the format.
• The actual data extraction (in this order):
  • From the VASP CHGCAR (text format).
  • From the exciting binary file. Noah already has an extraction method here.