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Thermodynamic phase transition of uranium trihydride: Role of electronic strong correlation

The electronic structure and thermodynamical properties of uranium trihydrides ($α$-UH$_{3}$ and $β$-UH$_{3}$) have been studied using first-principles density functional theory. We find that inclusion of strong electronic correlation is crucial in successfully depicting the electronic structure and thermodynamic phase stability of uranium hydrides. After turning on the Hubbard parameter, the uranium 5f states are divided into well-resolved multiplets and their metallicity is weakened by downward shift in energy, which prominently changes the hydrogen bond and its vibration frequencies in the system. Without Coulomb repulsion, the experimentally observed $α\mathtt{\rightarrow}β$ phase transition cannot be reproduced, whereas, by inclusion of the on-site correlation, we successfully predict a transition temperature value of about 332 K, which is close to the experimental result.