Enhanced angular overlap model for f-electron non-metallic systems

An efficient method of interpretation of the crystal field effect in non-metallic f-electron systems, the {\it enhanced angular overlap model} (EAOM), is presented. The method is established on the ground of perturbation expansion of the effective Hamiltonian for localized electrons and first principles calculations related to available experimental data. Series of actinide compounds, $An$O$_2$, oxychalcogenides, $An$O$X$ and dichalcogenides U$X_2$ where $X$ = S, Se, Te and $An$ = U, Np serve as a probe of effectiveness of the proposed method. An idea is to enhance the usual angular overlap model with {\it ab initio} calculations of those contributions to the crystal field potential, which cannot be represented by the usual angular overlap model (AOM). The enhancement leads to an improved fitting and makes the approach intrinsically coherent. In addition, the {\it ab initio} calculations of the main, AOM-consistent part of the crystal field potential allows one to fix the material-specific relations for the EAOM parameters in the effective Hamiltonian. In consequence, the electronic structure interpretation based on EAOM can be extended to the systems of the lowest point symmetries or/and deficient experimental data. Several examples illustrating the promising capabilities of EAOM are given.