database=prefix_rep_data.npz

prefix=amons or qm7,
rep=CM, SLATM, aCM, SOAP, FCHL.


structure: mol_prefix_labels, mol_prefix_ncharges, mol_prefix_rep

mol=vitc, vitd, qm9,
prefix=amons or qm7, # remove this?
rep=CMs, reps # combine these two?