Nature of the 5 f electronic structure of plutonium

Plutonium (Pu), in which the 5f valence electrons always wander the boundary between localized and itinerant states, exhibits quite complex crystal structures and unprecedentedly anomalous properties with respect to temperature and alloying. Understanding its chemical and physical properties, especially its 5f electronic structure is one of the central and unsolved topics in condensed matter theory. In the present work, the electronic structures of the six allotropes of Pu (including its alpha, beta, gamma, delta, delta', and epsilon phases) at ambient pressure are studied comprehensively by means of the density functional theory in combination with the single-site dynamical mean-field theory. The band structures, total and partial density of states, valence state histograms, 5f orbital occupancies, x-ray branching ratios, and self-energy functions are carefully studied. It is suggested that the alpha, beta, and gamma phases of Pu are typical Racah metals in which the atomic multiple effect dominates near the Fermi level. The calculated results reveal that not only the delta phase, but also all the six allotropes are archetypal mixed-valence metals with remarkable atomic eigenstate fluctuation. As a consequence, the 5f occupancy n(5f) is around 5.1-5.4, which varies with respect to the atomic volume and electronic correlation strength of Pu. The 5f electronic correlation in Pu is moderately orbital-dependent. Moreover, the 5f electrons in the delta' phase are the most correlated and localized.