Finally, absorption energies for the transition from the closed-shell ground state to the lowest charge-transfer state were calculated using CASSCF, XMS-CASPT2, and RMS-CASPT2, and are summarized in Table . These energies were computed using a non-equilibrium solvation model. First, the reaction field is generated at the closed-shell ground state with dielectric constant ε. The slow component is fixed with this reaction field, while the fast component is determined at the charge-transfer excited state using ε ∞ . The non-equilibrium energy for acetonitrile and water at the CASSCF level could not be obtained due to the quasi-degeneracy of the target state during SCF, so absorption energies were computed using nearly converged energy for reference (after 200 SCF iterations). A potential solution involves mixing density matrices of nearby states, but the oscillator strength of the transition from S 0 to any excited states other than the target charge-transfer state is smaller by two to three orders of magnitude (as shown by state interaction calculations 84 ), making this approach difficult to validate. Furthermore, since the ordering of states at the SCF and PT2 levels can be different, averaging other states at the SCF level does not necessarily correspond to averaging them at the PT2 level.