The structural, electronic, and optical properties of NpO2 and PuO2: a hybrid density-functional-theory study

Abstract

The structural, electronic, and optical properties of NpO2 and PuO2 have been investigated by means of the hybrid density functional theory (HDFT) using the full-potential linearized augmented plane (FP-LAPW) wave plus local orbitals (lo) method. The weight of exact Hartree-Fock (HF) exchange, α = 0.25, 0.35 and 0.40, are chosen for the hybrid density functional calculation. The obtained energy band gaps of NpO2 and PuO2 are 2.75 eV and 2.80 eV within α = 0.35 scheme, respectively, which are in excellent agreement with the recent experimental data. The calculated charge density and charge density differences in the (110) plane suggest the chemical bonds for the two actinide dioxides have main ionic character. Furthermore, the dielectric function and related optical parameters of the two compounds are firstly calculated using the HDFT method. In particular, the obtained refractive index n for PuO2 is consistent well with the experimental value in the wavelength range of 400 to 900 nm. We also predicted the effective number of electrons (n eff) contributing in the inter-band transitions reach a saturation value above 32 eV per unit cell for NpO2 and PuO2.