On the role of strong electron correlations in the surface properties and chemistry of uranium dioxide

Abstract

We report density functional calculations of the surface properties and chemistry of UO(2)(111) performed within the generalized gradient approximation corrected with an effective Hubbard parameter (GGA + U within Dudarev's formalism) to account for the strong on-site Coulomb repulsion between U 5f electrons. The variation of the properties of periodic slab models, with collinear ferromagnetic and antiferromagnetic arrangements of the uranium magnetic moments, was investigated while ramping up the effective Hubbard parameter from U(eff) = 0 eV, corresponding to standard density functional theory, up to U(eff) = 4 eV, the value that correctly reproduces the antiferromagnetic ground state of bulk UO(2). The chemical interactions of molecular water, dissociated water, dissociated oxygen and co-adsorbed molecular water and monatomic oxygen with the UO(2)(111) surface were also studied as functions of the U(eff) parameter. Calculations reveal that some of the key electronic and chemical properties controlling the surface reactivity are very sensitive to the value of this strong electron correlation parameter.

The layered uranyl silicate mineral uranophane-β: crystal structure, mechanical properties, Raman spectrum and comparison with the α-polymorph

“…The crystal structure was also optimized by adding the Hubbard correction with the parameter, U eff = 4.0 eV, determined by Weck et al 97 for uranium dioxide. The results, given in Table 1, show that the Hubbard correction does not introduce significant changes to the computed crystal structure.…”

Electronic structure of bulk AnO 2 (An = U, Np, Pu) and water adsorption on the (111) and (110) surfaces of UO 2 and PuO 2 from hybrid density functional theory within the periodic electrostatic embedded cluster method

“…Theoretical studies have disagreed as to whether molecular or dissociative adsorption is more energetically favourable on the (111) surface of UO 2 . Skomurski et al [22] and Weck et al [23] both found molecular adsorption to be more favourable, with adsorption energies of c. -0.7 (-0.25 for 1 monolayer (ML)) and -0.8 eV, whilst dissociative adsorption energies were lower with -0.4 (-0.22 for 1 ML) and -0.6 eV for a coverage of ½ ML. More recent studies have found dissociative adsorption to be more favourable at low coverage of ¼ ML, by 0.02 eV [24] and 0.07 eV [25], with an adsorption energy of -1.12 eV [24] and -0.68 eV [25] for dissociative adsorption.…”

Structural, mechanical, spectroscopic and thermodynamic characterization of the copper-uranyl tetrahydroxide mineral vandenbrandeite

“…134 The inuence of the Hubbard correction, 148 allowing for a correct description of the strong Coulomb repulsion between electrons in f orbitals, was also evaluated. The introduction of this correction, improving signicantly the description of uranium containing systems in which uranium exists with IV oxidation state, [149][150][151][152][153][154] seems not to be needed for vandenbrandeite as shown in Section 3. In fact, for a numerous set of materials in which uranium exists with VI oxidation state, the standard DFT description provides a reliable description of their structures and properties.…”