The authors study Cu2O (monovalent), CuO (divalent) and NaCuO2 (trivalent) as model compounds and try to relate the chemical shift and spectral properties to the formal valence (or oxidation state). As the valence increases, one imagines that the net charge on the Cu atom increases. The potential on the Cu site should then become more attractive and the binding energy of the core electrons increases. Such a chemical shift is observed for the model compounds mentioned above. The authors have performed band structure calculations using the density functional formalism in the local density approximation and the linear muffin-tin orbital (LMTO) method.
 

Japanese Journal of Applied Physics, Supplement, 32 212-16, 1993.