First-principles study of the hydrogen adsorption and diffusion on ordered Ni3Fe(111) surface and in the bulk

First-principles calculations based on density functional theory are performed to study the adsorption and diffusion of hydrogen on ordered Ni3Fe(111) surface and in the bulk. The adsorption of H2 molecule on surface is weak, but the adsorption of H atom on surface is strong. H2 decomposition on surface can easily take place and the largest barrier of H2 decomposition is 0.25 eV. The adsorption of H on surface and in the bulk is both exothermic relative to isolated H atom. The minimum barrier for H diffusion between two nearest sites on surface is 0.11 eV, indicating the H has good mobility on the surface. The minimum barrier for H diffusion from surface to the first subsurface is 0.78 eV. Once H atom diffuses into the first subsurface, it can more easily further diffuse into bulk with barrier values in the range 0.22-0.46 eV, which are very close to those values obtained in ordered bulk Ni3Fe. Moreover, the dependence of adsorption and diffusion properties on surface coverage is also discussed.