First-principles calculations of PuO2±x

The electronic structure of PuO2+/-x was studied using first-principles quantum mechanics, realized with the self-interaction corrected local spin density method. In the stoichiometric PuO2 compound, Pu occurs in the Pu(IV) oxidation state, corresponding to a localized f(4) shell. If oxygen is introduced onto the octahedral interstitial site, the nearby Pu atoms turn into Pu(V) (f(3)) by transferring electrons to the oxygen. Oxygen vacancies cause Pu(III) (f(5)) to form by taking up electrons released by oxygen. At T=0, the PuO2 compound is stable with respect to free oxygen, but the delicate energy balance suggests the possible deterioration of the material during long-term storage.