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

Abstract

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) calculations merged with dynamical mean‐field theory (DMFT). The results demonstrate that j=5/2 and j=7/2 manifolds are in the weakly correlated metallic and 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 of 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 the dual nature of 5f electrons, and the flexible electronic configuration of U ions. Finally, the so‐called quasiparticle band structure is also discussed.