Valence Fluctuation of Uranium Ions in Uranium Sesquinitride Revealed by Dynamical Mean-field Theory Merged with Density Functional Theory.

The electronic properties in particular the occupation number of 5f electrons and the valence state of U ions in uranium sesquinitride (U2N3) are studied by using density functional theory (DFT) merged with dynamical mean-field theory (DMFT). Calculation results demonstrate that j=5/2 and j=7/2 manifolds are in the weakly correlated metallic and the weakly correlated insulating regimes, respectively. The quasi-particle weights indicate that LS coupling scheme is more feasible for 5f electrons, which are not in the orbital-selective localized state. The weighted summation for the occupation probabilities of 5fn (n=0,1,2,3,4) atomic configurations suggests that 5f electrons have the inter-configuration fluctuation, or the mixed-valence state for U ions, together with an average occupation number of 5f electrons n5f~2.234, which is in good agreement with the electron localization function (ELF) and occupation analysis based on other DFT-based calculations. The 5fn-mixing-driven inter-configuration fluctuation might originate from such as the dual nature of 5f electrons, and the flexible electronic configuration of U ions. Finally, the so-called quasiparticle band structure is also discussed.