3d z 2 -orbital to a mixture between this and ligand ones. As a consequence, the wave function for the specie S 2+ changes from a 3d 9 -configuration to mixed 3d 9 /3d 10 . Measuring the expected value for the radius of the 3d z 2 component in the molecular orbitals ϕ s and ϕ d , Equations ( ) and ( ), we can track how the usual SA-CASSCF converged orbitals relate with the more restricted ones used in Figure . Figure ) shows the dependence of such orbitals with the weight used for the optimization. We notice that its size is similar to the ones for the isolated copper atom. The expected value for the radius of Cu + (3d 10 ) and Cu 2+ (3d 9 ) optimal 3d -orbitals are around 0.98 and 0.90 a 0 , respectively, indicated by the dotted lines in Figure ). Moreover, this molecular orbital quickly reaches the optimal size for the 3d 10 -occupancy, at 60% of the S + ground state weight, and is kept around this size for higher weights. This is somewhat expected, as the 3d -orbital size has much more influence over the S + ground state total energy than over the S 2+ one, as observed in Figure a). For ϕ d the radius is much larger than the one obtained for the isolated atom. This large size, together with its small coefficients, qualitatively depicted by c ′ d in Equation ( ), for weights smaller than 60%, indicates that those basis functions have only a polarization effect for small weights for S + . On the other hand, for high weights their radii and coefficients are comparable with those for ϕ s . Thus, the character that this 3d function has in the ϕ d orbital changes from polarization to valence orbital.