The performance of the developed method for stationary points and MECoIn was tested with the protonated Schiff-base (PSB3) in both vacuum and MeOH (methanol). To compare with previous CASSCF and MS-CASPT2 results using RISM, the reference wavefunction was obtained at the SA3-CASSCF(6e,6o) level (six π orbitals) with the 6-31G(d) basis set. As it is well known that PESs of MS-CASPT2 near crossing regions can show discontinuities, RMS-CASPT2 was used to investigate the topography of CoIns. For consistency with previous studies, a real level shift of 0.3 was employed.