Lastly, because these energy variations arise from distinct sets of orbital, their interaction must be considered as well. That way, varying both ligand and metal orbitals the energy change is of around 8.0 eV, Figure ), that is almost 1 eV larger than the sum of the energy variation from ligands and metal. Thus, these energy variations basically states the obvious, an optimal set of orbitals minimizes the energy in an energy minimization-based method. However, the important point here is: even with the destabilization of the configuration via the orbitals change there is no qualitative change in the wave function. That is, regardless of how well this state is described by the orbitals, its reference wave function remains as a pure d 10 -occupancy state. Therefore, in agreement with the CCSD results, we can define this state to be of a single reference and single d -occupancy character. In other words, its double d -shell effect is small and a double d -shell active We reinforce here that the ligand orbitals are relaxed in the presence of the fixed d -orbitals size in this case via a state specific calculation.