Thermodynamic Properties of Pu-O-H Compounds and Alloys from Density Functional Theory
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7KHUPRG\QDPLF3URSHUWLHVRI3X2+&RPSRXQGVDQG$OOR\VIURP'HQVLW\ )XQFWLRQDO7KHRU\ P. A. Korzhavyi1, L. Vitos1,2, and B. Johansson1,3 1
Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, SWEDEN 2 Research Institute for Solid State Physics and Optics, H-1525 Budapest, P.O. Box 49, HUNGARY 3 Condensed Matter Theory Group, Department of Physics, Uppsala University, Box 530, SE-751 21 Uppsala, SWEDEN $%675$&7 A theoretical approach has been developed that allows one to obtain thermodynamic properties of plutonium-based alloys and compounds from first-principles electronic structure calculations based on density functional theory. The approach is applied to study the defect structure in non-stoichiometric PuO2±δ. ,1752'8&7,21 The physics and chemistry of the actinide elements and their compounds form the scientific basis for rational handling of nuclear fuel. The key factor determining the physical and chemical properties of actinides and their compounds is the proximity of the 5f electrons to a localization/delocalization transition [1]. Theoretical treatment of this situation requires accurate exchange-correlation potentials going beyond the local density approximation, within which the localization tendency is typically underestimated. Several approaches have been proposed recently [2-4]. In this study we test the performance of more traditional (gradient-corrected) density functionals in the case of plutonium alloys and compounds, with a particular focus on the thermodynamic properties of non-stoichiometric PuO2±δ. This issue has recently received great attention in connection with the possibility to form hyperstoichiometric plutonium dioxide [5,6]. '(7$,/62)&$/&8/$7,216 Our spin-polarized, scalar-relativistic calculations of the electronic structure and total energy for Pu-Ga alloys and Pu-O-H compounds were based on density functional theory [7,8] and employed the Korringa-Kohn-Rostoker Green’s function (KKR-GF) method [9]. The electron density was calculated self-consistently within the multipolecorrected atomic-sphere approximation (ASA+M) and within the local density approximation (LDA) for the exchange-correlation potential [8,10]. The total energy was evaluated using the LDA self-consistent charge density, also including gradient corrections as formulated within the recently developed local Airy gas (LAG)
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4.8 fcc Pu−Ga, theory fcc Pu−Ga, experiment L12 Pu3Ga, theory L12 Pu3Ga, experiment L10 Pu3Ga, experiment
a0 (Å)
4.7
4.6
4.5
4.4
0
0.1 0.2 Atomic fraction of Ga
0.3
Bulk modulus (GPa)
60 fcc Pu−Ga, theory fcc Pu−Ga, experiment L12 Pu3Ga, theory
50
40
30
20
0
0.1 0.2 Atomic fraction of Ga
0.3
)LJXUH Calculated lattice parameters and bulk moduli of Pu-Ga alloys, in comparison with experimental data from Refs. [14,15].
approximation [11] and the generalized gradient approximation (GGA) [12]. An angular momentum cutoff Omax=3 was used, the multipole moments of the electron density were calcula
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