Analyzing the optimized orbitals using the usual SA-CASSCF protocol, we observe the same behavior as the PFRS results. That is, the singly occupied active orbital goes from an almost pure Figure : Results for the copper complex subsystem using the usual SA-CASSCF approach as reference wave function. (a): Electron Affinity dependence with the orbital optimization at SA-CASSCF and NEVPT2 levels of theory. Horizontal lines show the results for statespecific single reference calulations. (b): expected radius for the basis 3d z 2 -orbital that compose the active and closed orbitals described in Equations ( ) and ( ) by filled squares and hollow circles, respectively. Dotted lines indicate the expected radius value for the optimal d -orbitals of the isolated Cu 2+ (3d 9 ), bottom one, and Cu + (3d 10 ), top one.