First-principles study of α-Pu2O3

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.