Following an analysis for the orbital variation similar as done for S + , the S 2+ dependence with the d -orbital size is relatively small (around 1 eV), as shown in Figure ). We notice that such a result has precedent, for instance, that for the isolated iron atom the d 6 -occupancy state has a smaller total energy dependence with the d -orbital size than the d 7 one. On the other hand, the change in the ligand orbitals has a large impact over the S 2+ ground state energy, as shown in Figure ). With the variation of the ligand orbitals to better stabilize a Cu + center, the S 2+ ground state is destabilized in almost 6 eV. This destabilization shows that the Cu 2+ (3d 9 ) configuration has a larger dependence on the optimization of ligand orbitals than on the metal orbitals. This contrasts to what happens for the d 10 configuration, for which the dependence on ligands and metal orbitals are almost the same. Lastly, when both metal and ligand weights are gradually changed towards optimal orbitals for the S + (d 10 ) ground state, the S 2+ ground state is also highly destabilized as shown in Figure ). ii However, if compared with the previous graph, (b), this destabilization is slightly smaller. In other words, using the least optimal ligand and metal orbitals for the S 2+ (3d 9 ) wave function leads to a lower total energy for this state than if a semi-optimal set, composed of an optimal d 9 -orbital size with a set of ligand orbitals optimized around a Cu + center, is used. Such a result may appear contradictory, as the interaction between two effects that destabilize the states leads to a relative stabilization. However, this stabilization is caused by the relative energies between distinct d -occupancies and a qualitative change in the state wave function. Figure top schemes show, qualitatively, how the distinct d -occupancies configurations of the S 2+ ground states are stabilized depending on the orbitals. For instance, in all cases, the orbitals change toward optimal for S + (3d 10 ) destabilizes the expected S 2+ (3d 9 ) configuration, that is a Cu 2+ interacting with a neutral ligand ([Cu 2+ L] 2+ ), and stabilizes the more energetic S 2+ (3d 10 ) configuration, a Cu + ii We point out that the discontinuity from 90% to 100% is because the wave function optimized at this point has all orbitals double occupied. That way, active and closed orbitals can mix without affect the S + energy, but it affects the energy of the S 2+ ground state.