Hydrogen Adsorption on Low-Index Surfaces of B2 Titanium Alloys

Systematic first-principles calculations of hydrogen adsorption on two surfaces (001) and (110) of B2 titanium alloys with inclusion of complete relaxation of the system are performed for the first time within the electron-density functional theory. The equilibrium sites of hydrogen on metal surfaces are determined with respect to the surface termination and its orientation. It is shown that the hydrogen adsorption on the (001) surface in the series of titanium alloys under investigation is more preferred on the titanium-terminated surface. The relaxation effects change the adsorption energy by similar to 0.10-0.25 eV, although, in general, tendencies revealed for ideal films remain unchanged. Among the hydrogen sites studied on the TiMe(110) surface, the pseudo-threefold-centered F1 site with predominance of titanium atoms is most preferred for the alloys of the beginning of the series (TiFe, TiCo). For the TiNi, TiPd, and TiPt alloys, the adsorption energies in the F1 site and the titanium bridge site are nearly equal. The calculated curves of local and partial densities of states are used to explain the mechanisms of interaction between hydrogen and the surface.