I want to work with the Rayleigh-Ritz functions for CISD, CISDT, CISDTQ, etc. Does Psi4 have a way to access the Hamiltonian as a numpy array in the basis of the excited determinants? It feels like this technology must exist in the DETCI code- is it trivial to access it?
It looks like detci can construct Hamiltonian matrices through ciwave.cc:hamiltonian, but I can find no way to access that Python-side.