Self-interaction-corrected local spin density theory of5felectron localization in actinides

Abstract

The electronic structures of the actinide elements U, Np, Pu, Am, Cm, and Bk are investigated within the self-interaction-corrected local spin density approximation. This method allows us to describe a dual character of the 5f electrons, some of which occupy localized and corelike states, while the remaining 5f electrons hybridize and form bands. Based on energetics, the calculations predict delocalization and/or paramagnetism in the early actinides and localization and/or antiferromagnetism in the later actinides. The corresponding calculated equilibrium volumes are in agreement with the experimental values. For Pu and Am, the method wrongly predicts magnetic ordering, but we find that the paramagnetic state gives a better description of cohesive properties. Under compression, in the later actinides, a localization-delocalization transition happens gradually as more and more f electrons become bandlike with decreasing volume. Pu is already at this transition point at ambient conditions. Delocalization sets in for Am and Bk at a compression of V ϳ 0.75V 0 , for Cm at V ϳ 0.60V 0 , where V 0 is the equilibrium volume, and the transition is complete for V ϳ͑0.4-0.5͒V 0 in these three elements.Am. 23,32 The recent development of dynamical mean-field theory ͑DMFT͒, 33 combined with the LDA+ U approach, has enriched the field in terms of phenomena accessible to calculations, including both ground state cohesion, 24 phonons, 25 and photoemission. 26,27,34 However, most applications to date invoke the Hubbard Hamiltonian and inherit the uncertainties PHYSICAL REVIEW B 76, 115116 ͑2007͒

Self-interaction corrected local spin density calculations of actinides

“…For U and Np we find the non-magnetic band-f scenario to be energetically more favorable than the different localized/delocalized f-electron scenarios [23]. This ground-state configuration is in agreement with experiment, and indicates that correlations are relatively weak in these elements, thereby confirming the adequacy of the LSD picture for treating the electronic structure of the early actinides.…”

Atomic sizes from atomic interactions

“…This analysis shows that elements to the left of Pu have ''extrabonding" 5f electrons that contribute to bonding and are not localized. Those to the right have some localized (not ''extrabonding") (at NTP) as well as a few ''extrabonding" 5f electrons which indicates a coexistence of localized and band-like 5f electrons [19] even at ambient conditions. It is satisfying that the properties of heavy atoms may be interpreted reasonably well using the sizes r nZ c without requiring considerations of relativistic effects.…”

Valence fluctuations in thin films and theαandδphases of Pu metal determined by4fcore-level photoemission calculations

“…For the total energy of Pu metal LDA+ SIC calculations give the configurations from f 0 to f 4 almost degenerate, with f 5 slightly higher in energy, and f 6 much higher in energy due to the Coulomb repulsion. 33 Thus while these calculations give an apparent f count of ϳ2 for the metallic ground state of Pu metal, it gives f 6 in Am metal and f 7 in Cm metal as the lowest energy configuration. 33 Interestingly, the presence of nearly degenerate 5f levels in Pu metal indicates that a fluctuating valence state would be energetically favorable, which brings it in the realm of the Anderson impurity model.…”