Core-hole effect on XANES and electronic structure of minor actinide dioxides with fluorite structure

The authors investigated theoretically core-hole effects on X-ray absorption near-edge structures (XANES) of Np and Am L III in neptunium dioxide (NpO 2) and americium dioxide (AmO 2) with CaF 2-type crystal lattices using the all-electron full-potential linearized augmented plane-wave (FP-LAPW) method. The peak creation mechanism of XANES was shown by examining the electronic structures of these oxides, which indicated that core-hole screening was more marked for AmO 2 than for NpO 2 because of the difference in the charge transfer between these oxides. Furthermore, the results of charge density analysis suggested that the white line was assigned to the quasi-bound state composed of the localized Np d or Am d components and O components, and that the tail structure was created as a result of delocalized standing waves between the Np or Am atoms. ► Np L III XANES of NpO 2 and Am L III XANES of AmO 2 are theoretically examined. ► The core-effect in the measuremernt of these spectra was evaluated in detail. ► Core-hole screening by O p is more remarkable in AmO 2 than in NpO 2. ► Charge density analysis clarifies the peak creation mechanism of these spectra.