It was still difficult to identify the better MS-CASPT2 variants, but RMS-CASPT2-IPEA seemed to predict better relative energies in this investigation overall. One merit of RMS-CASPT2 over XMS-CASPT2 is a weaker dependence on the number of averaged states in the reference CASSCF calculation 36 because of the state-specific nature of the zeroth-order Hamiltonian. However, comparisons with other theoretical results may require extra care.