In Figure , a comparison of the results with and without IVO for RASCI (3h, 3e) and RASPT2 (3h, 3e) shows that the decrease in excitation energy from RASCI to RASPT2 is significantly larger without IVO. Specifically, the second-order perturbation energies (the total energy difference between RASCI and RASPT2) were always smaller with IVO than without. Since smaller perturbations are considered more reliable in perturbation theory, the RASCI results with IVO are likely to provide a more accurate description of the zeroth-order wavefunction than those without IVO. Furthermore, compared to the previous studies, the RASPT2 results with IVO are closer to the reported values for all calculated Ω states than those without IVO. This suggests that RASPT2 with IVO provides a more reliable description of the states than calculations without IVO.