First-Principles Study of Hydrogen Absorption on Zr(0001) Surface

The adsorption of H(2 )on Zr(0001) crystal surface was studied by the first-principles plane wave pseudopotential method within the density functional theory. By calculating the preferred adsorption sites, adsorption energy and electronic structure of Z(0001)/H-2 system, the microscopic mechanism for adsorption of H-2 on Zr(0001) surface was clarified. The results show that the favourable adsorption position of H-2 on Zr(0001) surface is the fcc site and its adsorption energy is 0.899 eV belonging to a strong chemical adsorption, and the two H atoms dissociated from H-2 molecules are finally stably adsorbed at the hollow and fcc sites on the surface of Zr(0001). There is a large amount of charge transfer between the adsorbed H atom and Zr (0001) surface, which results in the formation of ionic bond between H and Zr atom, and the typical covalent bonds between H and surface Zr form through the orbital hybridization of H is and Zr 5s, 4d. As a result, one can see that the chemical bonding between the H atom and the surface Zr atom is a characteristic mixture of the ionic and covalent bonding. In addition, the adsorption energy gradually increases with the increase of coverage. When the coverage increases to 4/5 ML, half of H atoms after the dissociation of H-2 are adsorbed on the subsurface of Zr(0001).