where m and w are, respectively, the metal and ligand weights in %, and the fitting residual is 0.13 eV. Therefore, the ligands weight has almost thrice the impact in the relative energy if compared with the metal ones. This suggests that, for a reliable description of this transition using the usual double d -shell active space approach, the inclusion of additional ligand orbitals would also be Although both the usual SA-CASSCF and our proposed step-wise optimization give us a systematic way to vary the relative stabilization between d -occupancies, there is no "end point" that leads to the "best" set of orbitals and nothing that prevents one to overshot the relative stabilization.