Hydrogen-induced reversal of surface rippling and diffusion energy barriers in Ni_3Al
The adsorption of hydrogen onto the (001) surface of Ni_3Al and the diffusion into the bulk are investigated using total-energy first-principles electronic structure calculations based on the full- potential linearized augmented plane wave (FLAPW) method. The atomic positions are relaxed employing the atomic force approach. It is found that the presence of hydrogen on the surface and subsurface causes a reversal of the surface rippling of the clean Ni_3Al surface, which returns to its normal condition when hydrogen diffuses into the bulk. The surface rippling reversal arises from the strong hybridization of the H 1s with the Ni 3d states. The diffusion energy barriers along several diffusion paths are calculated and the hydrogen is found to prefer to occupy nickel-rich octahedral interstices on the subsurface.