Electronic Structure Theory of the Ground State and Photoemission Spectra of Non-Magnetic δ-Pu, fcc-Am, and Pu-Am Alloys

The around-the-mean-field version of the LDA+U correlated band theory is applied to investigate the electronic and magnetic structure of d-Pu, Am, their alloys and compounds. It gives correct non-magnetic ground state for Pu and Am, and provides a good agreement with experimental equilibrium volumes and bulk moduli. For Pu-Am alloys, despite a lattice expansion caused by the Am atoms, neither tendency to 5f localization nor formation of local magnetic moments on Pu atoms in Pu-Am alloys are found. In order to access the experimental photoelectron spectra, we developed a straightforward and efficient procedure to perform dynamical mean-field (DMFT) calculations on the top of the static mean-field LDA+U approximation. Starting from self-consistent LDA+U ground state we included multiplet transitions using the Hubbard-I approximation. We obtained fairly good agreement with experimental photoelectron spectra of δ-Pu, Am, Pu0.25Am0.75 alloy, PuTe, and AmX (X=N,Sb). Our calculations show the importance of electron correlations beyond those which are included in conventional (LDA/GGA) band theory for Pu and Am based systems. Furthermore, we have shown that the three narrow features observed in the valence band spectra of Pu and majority of Pu compounds can be identified with the most intense atomic excitations (multiplets). The calculations explain that the atomic-like excitations can be observed even if the 5f states are not fully localized as in δ-Pu, and the atomic character fixes the characteristic energies such that similar features are found in spectra of diverse Pu systems. (authors)