Nonlocal Screening Effects in 2p X-Ray Photoemission Spectroscopy Core-Level Line Shapes of Transition Metal Compounds

We show that the 2p core-level line shapes of transition metal (TM) compounds are strongly influenced by the presence of more TM ions. Using calculations of clusters, involving more than one TM ion we explain the double period main line of the Ni 2p spectrum of NiO as well as the difference in line shape compared with Ni impurities in MgO and show the sensitivity of the line shape in NiO to surrounding defects. This intersite charge transfer screening also explains the wide asymmetric shape of the main line of the Cu 2p spectrum of CuO and the high-T(c) compounds.