Charge distribution and local and non-local screening effects studied by means of the Auger parameter and chemical state plots

We show that the Auger parameter can be helpful in the analysis of the screening mechanism in transition metal compounds. The position in the chemical state plots of different classes of compounds is discussed. The constancy of the Auger parameter for Cu(II) compounds is interpreted as further evidence of the electronic nature of the 2p3/2 final state. For Cu(I) compounds, as in the case of Zn(II) compounds (d10 electronic configuration), a large dependence of the Auger parameter on the chemical nature of the ligands suggests a non-local screening mechanism in the final state, i.e. a strong influence of electronic polarizability of the ligands on the relaxation energy. In this case, the extended s-p cation orbitals are involved in the screening process. The charge distribution in the initial state can be studied analytically or by using chemical state plots. It appears that the Auger parameter and the chemical state plots permit an accurate characterization of the ground-state electronic structure of cations in transition element compounds and of the screening mechanism in the final state.