DFT＋U calculations on [formula omitted](100) surface: thermodynamic stability and polarity compensation.

Employing the DFT+U framework we investigate the thermodynamic stability of U 3 O 8 (100) surface. The most stable structure is predicted to gradually turn from the under-stoichiometric 0 6 - to the over-stoichiometric 5 6 -slab as the oxygen chemical potential increases, showing a continuous surface oxidation process. Oxygen atoms are found to always firstly adsorb on the lower oxidized U ions. Due to the polarity compensation, significant modification of surface charge presents on considered terminations, which is transferred via both U-5 f and O-2 p states, implying the nature of U 3 O 8 as an intermediate state between the Mott–Hubbard and charge-transfer materials. It is also shown that the displacement of the outmost U 6 O 10 layer and the surface energy are strongly related to the redistribution of surface charge. The static effect between charged layers is the major factor which influences the layer displacement. The increase in surface energy is shown to be roughly linearly dependent on the amount of the surface charge transfer. [Display omitted] • The surface chemistry of U 3 O 8 (100) is dramatically influenced by polarity compensation. • U 3 O 8 (100) surface is predicted to transform from under- to over-stoichiometric as μ O increases. • U(2) is much more favorable in adsorbing oxygen atoms than U(1). • The charge transfer is accomplished via U-5 f and O-2 p states together. [ABSTRACT FROM AUTHOR]