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

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.