The adsorption properties of O atom and O2 molecule on UC(001) surface: A DFT study

Density functional theory calculations (DFT) were performed to study reactions on the uranium monocarbide (UC) surface when it is in contact with O atoms and O2 molecules. By studying the effects of the effective Hubbard parameter, Ueff, on surface energy, adsorption energy and work function, we identify that the con-ventional GGA method can give relatively reasonable results for surface systems. For the adsorption of O atom, it's found that the O atom prefers to be adsorbed at the hollow site for 1 and 0.5 monolayers (ML); however, the O atom tends to be adsorbed atop the U atom rather than the hollow site for 0.25 ML. We investigate the impact of coverages on surface adsorption using ab initio thermodynamics. The diffusion properties of O atoms on the surface are completely different according to different diffusion paths. As for O2, the surface adsorption of the O2 atop the U atom is non-dissociated for all horizontal and vertical adsorption approaches, but O2 prefers to dissociate into two O atoms for other sites. The analysis of charge density difference shows that O atoms only react with atoms on the surface and subsurface of UC. Co-adsorption studies on surfaces have shown that O atoms on the surface can hinder the chemisorption behavior of OH- while promoting the physical adsorption of water molecules on the surface.