Getting individual orbital energies of atoms

1

Hi Psi4 community,

I was wondering if there was a way to obtain the orbital energies corresponding to each atom in a system and also verifying if adding them up would give the total energy of the system?

I tried wfn.epsilon_a_subset("AO", "ACTIVE").print_out() which does print some floats with the length matching the total number of basis functions but they don’t seem to add up to the total SCF energy of the system…

Also there doesn’t seem to be a clear way to map these to the atoms of the molecule.

Appreciate any help I could get on this.

2
  1. Orbitals come from Hartree-Fock, which is a molecular orbital theory. Orbital energies belongs to molecular orbitals, which aren’t necessarily associated with any particular atom. If you want to associate an orbital energy with an atom, you need to tell me exactly how you want to do that.
  2. The Hartree-Fock energy is not the sum of orbital energies. The issue is the two-electron terms. You have orbital i interacting with orbital j contributing to both orbital energy i and orbital energy j, so the sum of the orbital energies will always double-count the two-electron terms.