Structure and properties of (Th, Pa)O2 and (U, Pa)O2 compound from density functional studies

Abstract:

Based on the first-principles of density functional theory, we use the PBEsol + U method to calculate the lattice and electronic structures, as well as mechanical and optical properties of ThO2, PaO2 and UO2 and (Th, Pa)O2 and (U, Pa)O2. The results of structural optimization indicate that the PBEsol + U method can provide more accurate lattice and mechanical parameters for actinide-based oxide ThO2, PaO2, and UO2. The calculation results show that the lattice parameters and the bandgaps of ThO2, PaO2, and UO2 are consistent with the experimental values and other related theoretical values. In the meanwhile, the lattice parameters of (Th, Pa)O2 and (U, Pa)O2 are between ThO2 and UO2, while predicting the band gaps of (Th, Pa)O2 and (U, Pa) O2 are also between ThO2 and UO2. Electronic properties calculations indicate that PaO2 and UO2 are Mott insulators, while ThO2 is a charge-transfer insulator. These are consistent with experiments and theoretical conclusions. (Th, Pa)O2 and (U, Pa)O2 have significant spin polarization effects near the Fermi energy level, and the bands are mainly occupied by Pa-5f and U-5f electronic state, respectively. Lastly, the real and imaginary parts and optical parameters of the optical dielectric functions of these systems are compared and analyzed.