All four methods predicted that the local topology of MECI-1 is peaked bifurcating as per the P and B parameters (Table ). However, this was not the case for MECI-2 (Table ), where the SA-CASSCF approach characterizes it as a peaked bifurcating CI (P = 0.05 and B = 0.39), while the CASPT2 variants as sloped single-path (5.00 < P < 5.50 and predicted the opposite energetic order for MECI-1 and MECI-2. The second best agreement was achieved using CAS(14e,11o): the largest difference from CAS(16e,13o) is about 2.5 kcal/mol despite the overestimation for MECI-2. Although it is difficult to finely control RASPT2, it can be used as a cost-effective alternative, especially considering the general expected accuracy of MRPTs. However, if N CSF for a CAS and RAS is similar, the CAS-based approach should be preferred.