Inter-Configuration Fluctuation for 5f Electrons in Americium Trichloride Studied Via Density Functional Theory Combined with Dynamical Mean-Field Theory

The electronic properties in particular the occupation number of 5f electrons and the valence state of Am ions in americium trichloride (AmCl3) are studied by using density functional theory (DFT) merged with dynamical mean-field theory (DMFT). We find that j=5/2, j=7/2 manifolds both are in the insulating regimes, resulting in the semiconducting band gap of about 0.837 eV, together with the weak Am 5f-conduction electrons hybridization and the localized 5f-derived spectra feature in the vicinity of the Fermi level. The weighted summation for the occupation probabilities of 5fn (n=3~7) atomic configurations suggests that 5f electrons have the inter-configuration fluctuation, or the mixed-valence state for Am ions, together with an average occupation number of 5f electrons n5f~5.182, corresponding to the valence state of Am3.818+ in AmCl3. The 5fn-mixing-driven inter-configuration fluctuation might originate from the complicated quantum mechanics processes 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 predicted.