DFT+U study of UO$_2$: Correct lattice parameter and electronic band-gap

Abstract: Hubbard-corrected density functional theory, denoted by DFT+U method, was developed to enable correct prediction of insulating properties for strongly-correlated electron systems. UO$_2$ is an example having O-$2p$, U-$6d$, and U-$5f$ incomplete electronic shells. Usually, researchers apply the Hubbard correction only to the localized incomplete $5f$ electrons of U atoms and succeed to predict insulating property and good geometric properties by tweaking the Hubbard-U parameter. However, it turned out that in such a way it was impossible to obtain reasonable values for both geometry and electronic band-gap at the same time. In this work, we show that it is possible to produce good values for those properties just by applying and tuning the Hubbard corrections to all incomplete shells of O-$2p$, U-$6d$, and U-$5f$.