Electronic Structure Calculations of Electronic and Structural Properties of Plutonium 115 Compounds
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Electronic Structure Calculations of Electronic and Structural Properties of Plutonium 115 Compounds J.M. Wills, R. Lizarraga, J.J. Joyce1, T. Durakiewicz1, J.L. Sarrao1, L. Morales2, and O. Eriksson.3 Equation of State and Mechanics of Materials Group, Los Alamos National Laboratory Los Alamos, NM 87545 USA. 1 Condensed Matter & Thermal Physics Group, LANL. 2 Nuclear Materials Technology Division, LANL. 3 Department of Physics, Uppsala University, Box 530, Sweden. ABSTRACT The 5f electronic states in elemental Pu and Pu compounds exhibit elements of both itinerant and localized behavior. Several first-principles calculations have been presented to describe this balance, differing in the manner in which electron correlation is included in the calculation. This paper describes a calculations performed with the Mixed Level Model (MLM), presenting calculated results for the two Pu compounds, PuRhGa5 and PuCoGa5. The MLM results are compared with other calculations and the differences discussed. INTRODUCTION The 5f electrons in elemental Pu are on the boundary between bonding (itinerate) and nonbonding (localized) behavior in the actinide series. As a function of band-filling, the light actinides (Th-Np) show a parabolic trend in equilibrium volumes and increasingly complex crystal structures consistent with itinerant, narrow-band 5f electronic states.[1] In contrast, the actinides past Pu (Am, …) show a trend in volumes with band-filling reminiscent of the lanthanide contraction, and have fairly simple ground state crystal structures. The special position of Pu in the actinide series is highlighted by the transition from the complex crystal structure of the low temperature monoclinic phase through a series of structural phases to the simple crystal structures of the fcc and bcc phases, and by the change in volume from the phase, consistent with light-actinide volume trends, to the volume of the -phase, approximately 25% larger than the volume, lying almost midway between -Pu and Am. First-principles calculations using Density Functional Theory (DFT) within the Local Density Approximation (LDA), particularly using the Generalized Gradient Approximation (GGA), have been successful in describing the structural properties of light actinides, including the correct calculation of ground state crystal structures.[2] Similar calculations for the actinides past Pu have also obtained fairly good results, provided the 5f electrons are treated as core-states. When applied to Pu, however, only the phase (the ground state) is well represented using these calculations. The high temperature phases, which experience with LDA tells us should be reasonably given, have equilibrium volumes and cohesive energies with little correlation to experiment. The calculations described, however, have been constrained to be non-magnetic, since most experimental evidence shows no indication of a local magnetic moment. It has been recognized for some time that calculations allowing spin-polarization, using the Local Spin D
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