Dropping highest virtual MOs in post-HF, in particular ADC(2), calculations

Dear All,

I wonder if dropping highest virtual orbitals is possible in post-HF, in particular ADC(2), calculations in Psi4. What is the keyword for that? I would appreciate very much an input example. Many thanks!

Best regards,

Not all method supports a frozen virtual approximation, but ADC does. The keyword is num_frozen_uocc. For an example input file:

molecule mol {
H 1 1.0 
H 1 1.0 2 104.5

set {
  reference rhf 
  basis cc-pvdz
  scf_type pk

set num_frozen_uocc 2

That said, be cautious about Psi4’s ADC results. There have been reports of answers from Psi not agreeing with those from Q-Chem. I don’t think we’ve traced the source of the disagreement yet.

Thank you very much for your answer and caveat regarding observed disagreement with QChem.

I also wonder, if it is possible to calculate transition dipole moments with ADC(2)?

Best wishes,