First-principles study of the structural and energetic properties of H atoms on a graphite (0001) surface

Electronic structure calculations based on spin-polarized density functional theory with the generalized gradient approximation and ultrasoft pseudopotentials are used to investigate the interaction between H atoms and a graphite (0001) surface. An asymmetric slab supercell approach is employed to model the graphite surface. The calculated equilibrium properties of bulk graphite, the hydrogen molecule and the graphite (0001) surface are all in good agreement with experimental data. The interaction of H with three high-symmetry sites on a graphite surface is considered. A broad and site-independent H physisorption region centered at around 4 Angstrom above the surface has a small binding energy of 8 meV. A localized stable chemical adsorption site can be found only when H is placed on the top site, with the help of substantial surface reconstruction. The reaction of a gas-phase H atom with an H adsorbed in the chemisorption site is then considered. Numerous total energy points are computed in the region of configuration space believed to be important for this Eley-Rideal reaction. Our results are in good agreement with the studies of Sidis and co-workers [Chem. Phys. Lett. 300 (1991) 157, Proc. Conf. H-2 in space]. Preliminary results from a quantum scattering calculation using a model potential energy surface fit to these points are presented. The trapping and recombination of H atoms on graphite surfaces is discussed, taking surface reconstructions into consideration. (C) 2001 Elsevier Science B.V. All rights reserved.