  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-$5f$.
