Next, a comparison between RISM calculations 32 in vacuum and MeOH was carried out for the protonated Schiff base (PSB3; C 5 H 6 NH + 2 ), using a reference wavefunction of SA3-CASSCF(6e,6o)/6-31G(d). The relative energies of three stationary points are summarized in Table . The "FC" entry corresponds to the energy of the Franck-Condon geometry (planar) in the ground state, "SP" refers to the energy of the saddle point (planar) in the first excited state, and "(CCT) CoIn " represents the S 0 /S 1 MECoIn around the C-C twisting coordinate. The optimized coordinates can be found in the Supporting Information. Although the CASSCF results in vacuum were mostly reproduced, the MS-CASPT2 results were already poorly reproduced in vacuum. The MS-CASPT2 calculations in this study and Ref. 32 were performed using different software packages, and there were some technical differences (e.g., internal contractions, electron repulsion integrals, and spatial symmetry), making direct comparison difficult. Nonetheless, we observe that the computed relative energies in this study systematically underestimate the values for FC and (CCT) CoIn , suggesting that qualitative discussion for these entries is possible. However, the discrepancy for SP is notably large. For the CASSCF results, we find that the trend of solvent-induced shifts is generally reproduced by PCM, though the shifts are overestimated by 0.1-0.2 eV for most entries. A significant excep-tion is found for (CCT) CoIn : the RISM calculation in Ref. 32 showed a minimal energetic shift (0.01 eV) due to the solvent, while PCM predicted a shift of 0.33 eV in this study. This discrepancy could be due to PCM systematically overestimating the shift or differences in the treatment of the solvent near the CoIn. The present study assumes full equilibration of the solvent, with polarization based on the averaged density of the crossing states. In contrast, the RISM calculation in Ref. 32 used a non-equilibrium model in a linear-response fashion. The equilibrium regime allows more degrees of freedom (e.g., solvent coordinates) to relax, leading to greater stabilization when the system equilibrates. If the deviation arises primarily from the different treatment of equilibration, we expect that PCM overestimates the stabilization and thus predicts lower relative energies than the systematic shift. However, the observed shift is quite similar. Another potential consequence of the differing equilibration regimes is that averaging the density matrices of the two states may partially cancel out the ESP from the solute, reducing the polarization of the ASC and thus the stabilization of the solute. While the dipole moment of charged systems is not uniquely defined, the dipole moments of the crossing states point in similar directions, meaning that this ESP cancellation should not be significant. The reason for the discrepancy of (CCT) CoIn is not clear at the moment, but overall, solvent effects are qualitatively captured by PCM at the CASSCF level, though improvements are needed, particularly in describing the crossing regions.