Electronic structure and chemical bonding in actinide oxides: Monoxides and dioxides of Np, Pu, Am, Cm and Bk

First-principles molecular cluster calculations of the electronic structure of actinide monoxides and dioxides have been carried out in the local density formalism. AcO₆^10- clusters representative of monoxides and AcO₈^12- clusters for dioxides (Ac = Np, Pu, Am, Cm and Bk) have been studied in spin-restricted and spinpolarized models, using the discrete variational method with numerical atomic basis functions. One-electron energy level diagrams, atomic configurations, charge and spin densities were obtained. It is found that significant covalent mixing of O 2ρ and Ac 5f atomic orbitais occurs for heavy actinide compounds, contrary to the assumption of free-ion models. X-ray photoelectron line shape calculations agree rather well with experimental data on the dioxides. Analogies between systematics of the energy levels of actinide and rare-earth compounds are discussed.