“…Starting with the work of Hubbard [11] a variety of theoretical methods have been invented to deal with this problem [12,13,14,15,16,17,18,19,20,21,22]. Major progress towards a quantitative description of 3d TM oxides has been made by the cluster method initiated by Fujimori and Minami [23,24,25,26,27] This takes the opposite point of view as compared to band theory, namely to abandon translational invariance and instead treat exactly -by means of atomic multiplet theory [28,29] -the Coulomb interaction in the 3d-shell of a TM-ion in an octahedral 'cage' of nearest-neighbor oxygen atoms. The angle-integrated valence band photoemission spectra calculated by this method are in excellent agreement with experiment [23,24,25,26,27].…”