Electronic structure of 3d transition metal compounds: systematic chemical trends and multiplet effects

The local electronic structure of 3d transition metal compounds is characterized by a few parameters, namely the ligand p to cation d charge transfer energy Δ, the dd Coulomb repulsion energy U, and the pd transfer integrals T. Values for these parameters deduced from the cluster model analysis of cation core level photoemission spectra are shown to exhibit systematic chemical trends as functions of cation atomic number, ligand, and cation valence. Physical properties of these compounds such as the magnitudes of the band gaps, pd covalency and the character of doped carriers, however, are not necessarily smooth functions of those variables but depend also on the nominal d electron number n due to the multiplet effects leading to the stabilization of the Hund's rule ground state. As an illustrative example, the electronic structure of valence-control Mn and Fe oxides is discussed.