The theory discussed in Section II C has been implemented in a development version of OpenMolcas. All CASSCF and CASPT2 results were obtained with it using the atomic compact Cholesky decomposition to generate an on-the-fly auxiliary basis set for the resolution-of-the-identity treatment of the electron repulsion integrals. All CASPT2 calculations were performed with the frozen core approximation and an imaginary level shift of 0.2i, and the IPEA shift parameter was set to either 0.00 (no IPEA) or 0.25 (IPEA) unless otherwise noted. The symmetry constraints were not used. Löwdin's canonical orthonormalization was employed for orthonormalizing the non-orthogonal ICB. Although any MS-CASPT2 variants could be used, XMS-CASPT2 and RMS-CASPT2 were employed in this study.