In the present comparison, MRCI used the state-averaged density matrix for constructing the Fock matrix, so the uniformity of the Fock matrix should be better reproduced with XMS-CASPT2. Moreover, RMS-CASPT2 has an additional source of non-invariance, so geometry optimizations with RMS-CASPT2 can be less stable than those performed with XMS-CASPT2. Although no rigorous comparison has been conducted, some extra geometry optimization steps were needed for RMS-CASPT2 compared with XMS-CASPT2. Regarding the difference between behaviors of geometry optimization without and with IPEA shift, geometry optimizations with IPEA shift were slightly less stable than those without it and required some extra steps, even though the instability was not critical for determining min-imum energy and MECI structures.