Electronic structure and ionicity of actinide oxides from first principles calculations

TL;DR

This study uses first-principles calculations to analyze the electronic structure and ionicity of actinide oxides, revealing how f-electron localization correlates with oxidation states and stability across different compounds.

Contribution

It provides a detailed first-principles analysis of actinide oxides, highlighting the relationship between electron localization, oxidation states, and stability, which was not thoroughly characterized before.

Findings

AO2 compounds are metallic due to A(2+) configuration.

Dioxide is the most stable oxide from Np onwards.

Localization of f-electrons correlates with oxidation state and stability.

Abstract

The ground state electronic structures of the actinide oxides AO, A2O3 and AO2 (A=U, Np, Pu, Am, Cm, Bk, Cf) are determined from first-principles calculations, using the self-interaction corrected local spin-density (SIC-LSD) approximation. Emphasis is put on the degree of f-electron localization, which for AO2 and A2O3 is found to follow the stoichiometry, namely corresponding to A(4+) ions in the dioxide and A(3+) ions in the sesquioxides. In contrast, the A(2+) ionic configuration is not favorable in the monoxides, which therefore become metallic. The energetics of the oxidation and reduction of the actinide dioxides is discussed, and it is found that the dioxide is the most stable oxide for the actinides from Np onwards. Our study reveals a strong link between preferred oxidation number and degree of localization which is confirmed by comparing to the ground state configurations of the corresponding lanthanide oxides. The ionic nature of the actinide oxides emerges from the fact that only those compounds will form where the calculated ground state valency agrees with the nominal valency expected from a simple charge counting.