First-Principles Energetics of Some Nonmetallic Impurity Atoms in Plutonium Dioxide

Abstract

The energetics of some typical non-metallic impurity atoms (H, Ne, Cl, Ar, Kr and Xe) in PuO 2 are calculated using a projector augmented-wave method under the framework of density functional theory. The Hubbard parameter U and van der Waals corrections are used to describe the strongly correlated electronic behavior of f electrons in Pu and weak interactions of rare gases, respectively. Three incorporation sites of for impurity atoms, i.e., octahedral interstitial, O vacancy, and Pu vacancy sites, are considered. The results indicate that the energetics of impurity atoms depend significantly on the incorporation sites and on atomic properties such as atomic radius and electron affinity. Almost all impurity atoms considered here are energetically unfavorable at the three incorporation sites, with the exception of the F atom at the octahedral interstitial and O vacancy sites. The trends of incorporation energies of rare gas atoms generally reflect a size effect. Furthermore, charge-transfer analysis reveals that the valence electrons can be polarized more easily with increasing atomic number of rare gas elements. Finally, electronic structures of these systems containing impurity atoms also exhibit general trends in their relative stability and chemical bonding character.

First-principles DFT +U calculations on the energetics of Ga in Pu, Pu2O3 and PuO2

“…An effective U (U eff = U À J; i.e., the difference between the Coulomb U and exchange J parameters, hereafter referred to as U) value of 4 eV is selected for the localized Pu 5f electrons. This value has been demonstrated by our previous calculations to be reasonable in reproducing the experimental lattice parameter, bulk modulus and band gap of PuO 2 , along with the reaction energies related to the formation of hyperstoichiometric Pu oxides [34,35]. Additionally, we test U values in the range of 3-6 eV for calculations related to PuO 2 and PuO 2.25 .…”

“…Above all, in terms of other researchers' and our previous calculations on Pu-based materials, especially on Pu oxides [3,15,34,35,[56][57][58], we briefly discuss the general features of the electronic structures of Pu, Pu 2 O 3 and PuO 2 with or without impurity atoms. The most remarkable feature of the electronic structure of metallic Pu lies in the presence of strong localized 5f states just below the Fermi energy (E F ), indicating that the localized 5f states do not contribute to chemical bonding or hybridization with other electronic states.…”

“…Therefore, in most cases regarding the issue of Pu surface science, hyperstoichiometric Pu oxides are usually excluded from the discussion. For the influencing effects of impurity atoms in Pu oxides, our previous calculations on a series of nonmetallic impurity atoms in PuO 2 showed that the perturbation from most of the impurity atoms could result in instability of the host, and only the strongest oxidant F with small atomic radius and large electron affinity could stabilize the host [35].…”

“…), we calculated the energetics of some typical nonmetallic impurity atoms (i.e., H, He, B, C, N, O, F, Ne, Cl, Ar, Kr and Xe) in PuO 2 [34,35]. A general trend in the relative stability of the impurity atoms was obtained by the comparison of atomic basic properties (i.e., atomic radius and electron affinity) with the calculated energetics and electronic states.…”

Dissociation Mechanism of Water Molecules on the PuO2(110) Surface: An Ab Initio Molecular Dynamics Study

“…The DFT + U approach is one of the most popular methods that allow correct treatment of systems containing strongly correlated electrons. By addition of an energy term of the effective Hubbard parameter, the antiferromagnetic Mott insulator feature and structural parameters of PuO 2 are well described. − Several previous studies had focused on the properties of plutonium-oxide surfaces. − Jomard and Bottin investigated the influence of electronic correlations on thermodynamic stability of PuO 2 surfaces in ref and also pointed out that the electronic structure of the insulating PuO 2 surfaces can be well described within the DFT + U method, which is a prerequisite to explore chemical reactions on the PuO 2 surfaces. Sun et al further reported the effects of thickness and oxygen vacancy on the stability and chemical activity of the PuO 2 surfaces, where the spin–orbit coupling (SOC) interaction was considered .…”