First-principles study of H2 adsorption and dissociation on Zr(0001)

The adsorption and dissociation of H-2 molecules on the Zr(0001) surface are systematically investigated by using density functional theory within the generalized gradient approximation and a supercell approach. After geometry optimization, the most stable equilibrium adsorption state is found to be along the top-y entrance. By calculating the adiabatic potential energy surface, the chemisorbed molecular adsorption states are also identified to be along the parallel channel at the top site. The electronic properties of the stable chemisorbed molecular state are analyzed, which show that the interaction between the molecule and substrate is of covalent characteristic with a sizeable charge redistribution. On the other hand, the hcp site is turned out to be the most stable equilibrium adsorption site for hydrogen atom on Zr(0001) surface after the dissociation of H-2. The dissociation energetics of H-2 are studied by calculating the potential energy surface and the minimum energy path of the transition state is determined by using the climb image nudged elastic band method, wherein the fcc-y channel is found to be most stable and favorable for dissociative adsorption of H-2 among the five possible dissociative paths. Remarkably, we find that the adiabatic dissociation process of H-2 is an activated type but with a small energy barrier, which is well consistent with the macroscopic phenomenon that the zirconium metal is easily hydrogenated. (C) 2011 Elsevier B.V. All rights reserved.