DFT + U Study of Uranium Dioxide and Plutonium Dioxide with Occupation Matrix Control

Abstract

DFT + U with occupation matrix control (OMC) is applied to study computationally bulk UO2 and PuO2, the latter for the first time. Using the PBESol functional in conjunction with OMC locates AFM and NM ground states for UO2 and PuO2, respectively, in agreement with experimental findings. By simulating the lattice parameter, magnetic moment, band gap, and densities of states, U = 4.0 eV is recommended for AFM UO2, yielding data close to experiments for all considered properties. U = 4.5 and 4.0 eV are recommended for NM and AFM PuO2, respectively, though much larger U values (c. 10 eV) are required to yield the most recently reported PuO2 band gap. For both oxides, several excited states have similar properties to the ground state, reinforcing the need to employ OMC wherever possible.