The Hessian matrix, needed for vibrational frequency analysis, was obtained by a semi-numerical approach, in which analytic first-order geometrical derivatives were computed for displaced geome-tries. In the previous study, ZPVEs obtained with NEVPT2 were used for CASPT2, but they were computed using individual CASPT2 methods in this study. The deviations from the experimental 0-0 transition energies with CASSCF, (partially contracted) NEVPT2, XMS-CASPT2, and RMS-CASPT2 are summarized in Table .