MOLECULAR CLUSTER THEORY OF CHEMICAL BONDING IN ACTINIDE OXIDES.

The electronic structure of actinide monoxides AcO and dioxides AcO//2, where Ac equals Th, U, Np, Pu, Am, Cm and Bk has been studied by molecular cluster methods based on the first-principles one-electron local density theory. Molecular orbitals for nearest neighbor clusters AcO//6**1**0** minus and AcO//8**1**2** minus representative of monoxide and dioxide lattices were obtained using non-relativistic spin-restricted and spin-polarized Hartree-Fock-Slater models for the entire series. Fully relativistic Dirac-Slater calculations were performed for ThO, UO and NpO in order to explore magnitude of spin-orbit splittings and level shifts in valence structure. Self-consistent iterations were carried out for NpO, in which the NpO//6 cluster was embedded in the molecular field of the solid. Finally, a moment polarized model which combines both spin-polarization and relativistic effects in a consistent fashion was applied to the NpO system.