Dual 5f character in two allotropes of uranium trihydride studied via a first principles calculation

Abstract

A first principles calculation on the electronic properties of α- and β-UH3 is implemented by using a many-body method merging density functional theory (DFT) with dynamical mean field theory (DMFT). Results show that α- and β-UH3 are both in mixed-valent metallic states with an average occupation of 5f electrons nf about 2.418 and 2.520, respectively, and exhibiting strong valance fluctuation due to the quantum superposition of 5f2 and 5f3 configurations in the ground state. The spectrum function demonstrates that U 5f electrons possess the dual characters, i.e., the localized and itinerant behaviors, and the localized 5f counts are 1.106 and 1.112 for α- and β-UH3, respectively, which is well in accord with the experimental observations. The imaginary part of the impurity Green functions reveals that U 5f j = 5/2 and j = 7/2 states both exhibit the metallic and insulating characteristics, respectively. The quasi-particle weight establishes that U 5f j = 5/2 and j = 7/2 states are in the moderately and weakly correlated regimes, respectively, and jj coupling scheme is more feasible as compared to the intermediate coupling (IC) or the Russel-Saunders (LS) coupling regime.