The smoothness of XMS-RASPT2 was also investigated using three active spaces for a transoid MECI of butadiene (structure k in Ref. 77): CAS(4e,4o), RAS(4e,4o)/(0e,0o)/2, and RAS(4e,4o)/(2e,2o)/1. We found small distortions even with CASPT2-IPEA, in particular, for a relatively large x and ŷ. This was not seen in the previous XMS-CASPT2 and -RASPT2 result for the same system without IPEA shift. Irregularities in the left panel were rather small, and geometry optimizations for these MECIs using CASPT2-IPEA and RASPT2-IPEA indeed did not exhibit any difficulties. In RAS(4e,4o)/(0e,0o)/2 (right panel in Figure (B)), there were three noticeable discontinuities (∼5 kcal/mol). As expected, PESs described with RASPT2 could have more irregularities and discontinuities than those described with CASPT2 and more than those with IPEA shift, although it is possible to find MECIs using RASPT2-IPEA. In this study, no further RASPT2 calculations were performed; the applicability of RASPT2-IPEA for MECIs should be further investigated in future work.