All RAS calculations use a (4,4) active space and the hole-particle (h,p) algorithm that was outlined in Section II A, starting from a quintet ROHF reference state. In order to use the CT version of RAS-SF, the ROHF orbitals were localized using the Pipek-Mezey procedure. Core orbitals are not correlated (i.e., frozen core approximation). The basis set is either 6-31G*, cc-pVDZ, or cc-pVTZ, as indicated in the discussion that follows. Q-Chem's RAS algorithm uses a resolution-of-identity (RI) approximation for the integrals. For the auxiliary (density fitting) basis set, we use either the ones designed for use with cc-pVXZ, or else that designed for use with the Ahlrichs SVP basis set. In Q-Chem, these two basis sets are called RIMP2-cc-pVDZ and RIMP2-VDZ, respectively.