In this sense, the assignment of oxidation state becomes ambiguous. To assign the copper oxidation state, a localized orbital CAS configuration interaction (CASCI) calculation was performed. This approach allows for a valence-bond-like interpretation of the wave function that has been successfully in the literature, by the authors and others, to obtain a valence bond (VB)-like interpretation of the CASSCF wave function in which covalent contributions to bonding are removed via orbital localization and the CASSCF electron configurations can be recomputed in a new basis that is more easily related to changes in oxidation states. An example of using this approach for the straightforward π system in ethylene is given in the Supporting Information of reference 49.