ELEMENTAL AND MIXED ACTINIDE DIOXIDES: AN AB INITIO STUDY

We present a systematic study of the electronic, geometric, and magnetic properties of the actinide dioxides, UO2, PuO2, AmO2, U0.5Pu0.5O2, U0.5Am0.5O2 and Pu0.5Am0.5O2. For UO2, PuO2 and AmO2, both density functional and hybrid density functional theory (DFT and HDFT) have been used. The fractions of exact Hartree-Fock (HF) exchange chosen were 25% and 40% for the hybrid density functional. For U0.5Pu0.5O2, U0.5Am0.5O2 and Pu0.5Am0.5O2, only HDFT with 40% exact HF exchange was used. Each compound has been studied at the nonmagnetic, ferromagnetic and anti-ferromagnetic configurations, with and without spin-orbit coupling (SOC). The lattice parameters, magnetic structures, bulk moduli, band gaps and density of states have been computed and compared to available experimental data and other theoretical results. Pure DFT fails to provide a satisfactory qualitative description of the electronic and magnetic structures of the actinide dioxides. On the other hand, HDFT performs very well in the prediction and description of the properties of the actinide dioxides. Our total energy calculations clearly indicate that the ground-state structures are anti-ferromagnetic for all actinide dioxides considered here. The lattice constants and the band gaps expand with an increase of HF exchange in HDFT. The influence of SOC is found to be significant.