Structural, thermodynamic, and electronic properties of plutonium oxides from first principles

Abstract

We report ab initio calculations of the structural, electronic, optical, and thermodynamic properties of plutonium oxides (${\text{PuO}}_{2}$ and $\ensuremath{\beta}{\text{-Pu}}_{2}{\text{O}}_{3}$). In order to describe the basic features of the electronic structure, a method suited to take into account strong local correlations has to be used. We apply the local density approximation/generalized gradient approximation ($\text{LDA}/\text{GGA})+U$ approximations to these compounds and compare them with the calculations of Sun et al. [J. Chem. Phys. 128, 084705 (2008)]. Whereas a good agreement is obtained for ${\text{PuO}}_{2}$, our LDA and $\text{LDA}+U$ results differ strongly from this study in the case of ${\text{Pu}}_{2}{\text{O}}_{3}$. In particular, the effect of the Hubbard parameter $U$ on the volume is qualitatively and quantitatively different. Moreover, thermodynamic quantities differ. We thus focus our study on ${\text{Pu}}_{2}{\text{O}}_{3}$ and emphasize the importance of a careful and systematic search of the ground state in $\text{LDA}+U$: In particular, different hints for the occupation matrices corresponding to the electronic configurations allowed by symmetry have to be tried. This procedure is absolutely necessary to find the absolute minimum of the energy. Reliable and accurate quantitative results are given for ${\text{Pu}}_{2}{\text{O}}_{3}$. We thus recover a more physical behavior coherent with calculations on other systems, such as cerium oxides.