Electronic structure of transition metal compounds: Photoemission experiments and model Hamiltonian calculations

We discuss the case of NiO in detail to exemplify the use of photoemission experiments and model Hamiltonian calculations in order to unravel the electronic structure of transition metal compounds. Then we discuss the transition metal compounds and their metallic/nonmetallic properties in terms of a generalized phase diagram as a function of the Coulomb interaction strength and charge transfer energy. Finally, we discuss the electronic structure of the high-$T_c$ cuprate superconductors as deduced from photoemission experiments and model calculations in relation to the above-mentioned phase diagram