Surface properties of uranium dioxide from first principles

Computational modeling of the properties of clean uranium dioxide (UO₂) surfaces is a necessary step to modeling and understanding UO₂ surface mechanisms such as corrosion and the formation of complex species via environmental gas adsorption. In this work, all-electron hybrid density functional theory, including spin–orbit coupling effects, has been used to study the evolution of the work function, surface energy, incremental energy, and band gap of the clean (1 1 0) and (1 1 1) surfaces of UO₂ with respect to the system size. At five layers of formula units and beyond the surface properties of UO₂ converge. The estimated work function, surface energy, and band gap of the (1 1 1) surface were 3.5 eV, 0.97 J/m², and 1.2 eV respectively; the corresponding values for the (1 1 0) surface were 2.2 eV, 1.76 J/m², and 0.65 eV respectively. The localization of the 5f electron states is pronounced at the top surface layer while bulk-like behavior is exhibited at and below the subsurface layer. The Mott–Hubbard type insulating behavior in the bulk is retained in the surfaces, albeit with a smaller band gap