Mixed RHF and ROHF

1

Dear friends,

I am calculating the interaction energy between a molecule and O2.

O2 has unpaired electron pairs, in this case ROHF is ok. For the other molecule, which does not have unpaired electron pairs, RHF is ok.

Since Psi4 doesn’t allow a mixed reference (ROHF for O2 and RHF for the other molecule), is it ok to use ROHF for the dimer?

Best,

2

Yes, that’s the correct procedure. ROHF applied to a closed-shell system simplifies to RHF. If you want to be paranoid, write out orbitals using Molden and verify that the open-shell orbital is largely localized on O2. As long as it is, you should be fine.

3

Many thanks for the reply @jmisiewicz!

Best,