First-principle Studies Of Oxygen Adsorption On The γ-U(110) Surface

As one of the most important natural radioactive elements,uranium（U） is well known because of its use as a nuclear reactor fuel.Uranium has special physical and chemical properties due to its complex electronic structures and strong correlation of 5f electrons.The special valence electron structures make it to be extremely vulnerable to chemical and electrochemical action of environmental mediators.One of the fundamental problems of uranium storage and practical applications is surface corrosion as a result of oxidation reactions in the atmosphere.Although uranium oxidizing has received considerable attentions for years,the process of oxide formation,which begins with oxygen adsorption on uranium surface is not yet well understood.Compared with experiments,first-principle simulation calculation can investigate the interaction process at the atomic level,it has significant advantages in time cost,material cost and safety.In this study,we use first-principle molecular dynamics（FPMD）simulations and density-functional theory（DFT）static calculations to investigate the kinetics and energetics of oxygen absorption onγ-U（110） surface and Mo-dopedγ-U（110）surface.The FPMD simulations shows that O₂ will spontaneously dissociates into separate O atoms,and finally adsorbed on the surface.The doping Mo can change the final adsorption sites of O atoms.In addition,we found that temperature can accelerate O₂ dissociation onγ-U（110） surface.The calculation of adsorption energies shows that the most preferred site for O atoms on theγ-U（110） surface is the short bridge site,followed by the 3-fold hollow.The doping Mo will decrease the adsorption energies of all the adsorption sites.With Mo-doping,the most preferred site for O atom is still short bridge.But,the second preferred adsorption site become long bridge.For clean and Mo-doped surfaces,the on-top is the least preferred adsorption site for atomic oxygen.Through calculations of diffusion pathways,we found Mo-doping raise the energy barrier for O atom diffusion on the surface.By the calculated segregation energies,it is found that the Mo atom prefers to locate in γ-U“bulk” rather than the top layer of the surface.