  We systematically investigate the electronic structure, magnetic order, and
valence states of $\alpha$-Pu$_{2}$O$_{3}$ (\emph{C}-type) by using
first-principles calculations. $\alpha$-Pu$_{2}$O$_{3}$ can be constructed from
PuO$_{2}$ by removing 25% oxygen atoms. Our results show that the Pu 5\emph{f}
orbitals are further localized after removing ordered oxygen atoms. This
phenomenon is demonstrated by the combined fact that (i) the volume per unit
cell expands 7% and (ii) the corresponding magnetic moments and valence states
for Pu ions increase and decrease, respectively. According to the density of
states and charge density distribution analysis, PuO$_{2}$ is found to be more
covalent than $\alpha$-Pu$_{2}$O$_{3}$, which is also because of the more
localization of 5\emph{f} orbitals in the latter. The calculated lattice
constants, bulk modulus, and electronic structures for PuO$_{2}$ and
$\alpha$-Pu$_{2}$O$_{3}$ are consistent well with experimental observations.
