By combining the local density approximation (LDA) with dynamical mean field theory (DMFT), we report a systematic analysis of the spectral properties of δ-plutonium with varying 5f occupancy. The LDA Hamiltonian is extracted from a tight-binding (TB) fit to full-potential linearized augmented plane-wave (FP-LAPW) calculations. The DMFT equations are solved by the exact quantum Monte Carlo (QMC) method and the Hubbard-I approximation. We show the strong sensitivity of the spectral properties to the 5f occupancy, which suggests using this occupancy as a fitting parameter in addition to the Hubbard U. By comparing with PES data, we conclude that the “open shell” 5f 5 configuration gives the best agreement, resolving the controversy over 5f “open shell” versus “close shell” atomic configurations in δ-Pu.

The electronic structure of single crystal UO2 and polycrystalline δ-Pu is examined using photoelectron spectroscopy. These two actinide materials exhibit properties consistent with the 5f electrons at the threshold between localized and itinerant character. The results for δ-Pu may be viewed as the 5f electrons exhibiting a dual nature with some fraction of the 5f levels localized and not participating in the bonding while the other fraction of 5f character is involved in bonding and hybridization with the conduction electrons. For UO2 where angle-resolved photoemission is available, one observes dispersion in the 5f features indicative of the 5f electrons being influenced by the periodic potential of the lattice rather than purely influenced by the site to which the 5f electrons are generally localized.