Electronic Structure and Photoemission in Plutonium Chalcogenides
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1104-NN02-06
Electronic Structure and Photoemission in Plutonium Chalcogenides Alexander Shick1, Ladislav Havela2, and Thomas Gouder3 1 Inst. of Physics ASCR, Prague, Czech Republic 2 Dept. of Cond. Matter Physics, Charles University, Prague, Czech Republic 3 Institute for Transuranium Elements, Karlsruhe, Germany ABSTRACT The electronic structure of Pu chalcogenides is investigated making use of static around-meanfield LDA+U and dynamical LDA+HIA (Hubbard-I) methods. The LDA+U calculations provide correct non-magnetic ground state for PuX (X = S, Se, Te) with 5f-manifold non-integer filling (from approx. 5.6 in PuS to 5.7 PuTe). This is an indication of a mixed valence ground state which is a combination of f 5 and f 6 multiplets. The photoelectron spectra are calculated in good agreement with experimental data. The three-peak feature near EF attributed to 5f-manifold is well reproduced by LDA+HIA, and follows from mixed valence character of the ground state. INTRODUCTION Plutonium chalcogenides PuS, PuSe and PuTe studied before [1,2] belong to NaCl structure type materials. They exhibit semi-metallic and weakly paramagnetic behaviour at variance with Pu pnictides and also with U and Np chalcogenides. Here we focus on theoretical studies of essential bulk properties as well as photoelectron spectra (PES) of Pu chalcogenides, and on implications for δ-Pu and other Pu systems. During last few years, electronic structure calculations of Pu and Am based on the conventional band theoretical methods (the local density or generalized gradient expansion approximations LDA/GGA to the density functional theory) could not explain essential experimental data. While the LDA/GGA band structure calculations predict a local magnetic moment (ordered or disordered) to form at the Pu [3] and Am [4] atoms, none of them were seen in the experiment [5]. The same approaches attempted to evaluate the photoemission spectra and electronic specific heat in Pu and Am using single-particle LDA/GGA densities of states (DOS), incorrectly assuming weak electron correlation character of 5f systems at the borderline between the localized, nonbonding, behaviour and the bonding situation of electronic bands. Here we apply a DMFT based computational scheme based on multi-orbital Hubbard-I approximation (HIA) [6,7] including the spin-orbit coupling (SOC), which explicitly accounts for the atomic-like multiplet transition excitations in PuX (X = S, Se, Te) compounds [8]. Starting from the non-magnetic ground state calculated with the static mean-field AMFLSDA+U approximation [9], we obtain excitation spectra of PuX in a reasonably good agreement with PES, in support of the atomic-like origin of the electronic excitations in these materials.
THEORETICAL METHOD We start with the multi-band Hubbard Hamiltonian [6] H=H0+Hint, where H0=
∑
0
i,j,α,β
†
Hiα,jβciαcjβ=
∑
0
k,α,β
†
Hα,β(k)cα(k)cβ(k)
(1)
is the one-particle Hamiltonian found from ab initio electronic structure calculations for a periodic crystal. The indices i,j label the lattice sit
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