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

TL;DR

This study uses first-principles calculations to show that strong electronic correlations are essential for accurately modeling the phase transition and thermodynamic properties of uranium trihydrides, aligning well with experimental data.

Contribution

It demonstrates the importance of including strong electronic correlation effects in first-principles calculations to accurately predict phase stability and transition temperatures of uranium hydrides.

Findings

Inclusion of Hubbard U reproduces the $ ext{α} ightarrow ext{β}$ phase transition.

Strong correlation effects alter uranium 5f states and hydrogen bonding.

Predicted transition temperature (~332 K) closely matches experimental value.

Abstract

The electronic structure and thermodynamical properties of uranium trihydrides ($\alpha$-UH$_{3}$ and $\beta$-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 $\alpha\mathtt{\rightarrow}\beta$ 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.