Support frozen core

[haakoek]

This is done naively by just restricting the occupied indices, i.e.,
occ = slice(0,n) #n is the number of elctrons, is replaced with
occ = slice(n_frozen, n) #n_frozen is the number of frozen core orbitals.

PyScf has frozen core support that we can test groundstate energies against.

[Schoyen]

Is it really that simple?

[haakoek]

Naively yes, in practice maybe not, it should affect the shape/size of the amplitudes as well, i.e., system.n effectively becomes n-n_frozen (I think).

[Schoyen]

This is related to HyQD/quantum-systems#40.