Theoretical Description of Hydrogen Atom Scattering off Noble Metals
I have constructed a full dimensional potential energy surface (PES) for a H atom interacting with a Au(111) surface by fitting the analytic form of the Effective Medium Theory to density functional theory (DFT) energies. The fit used energies of the H Au system with the Au atoms at their relaxed lattice positions as well as configurations with the Au atoms displaced from these positions. The procedure provides an accurate treatment for displacements of Au atoms and compares well to DFT energies for scattering of H atoms obtained from ab initio molecular dynamics (AIMD) In adiabatic molecular dynamics simulation, the PES is capable of reproducing the energy loss behavior of AIMD. The effective medium theory also provides the background electron density which makes it possible to treat the excitation of energetically low lying electron hole pairs self consistently in the frame of local density friction approximation. I have tested various incidence conditions for H scattering from Au(111) and find that in all cases, the energy loss by electron hole pair excitation is by far the most efficient pathway and dominates the scattering behavior and influences the adsorption mechanism significantly. Comparison to experiment confirms that energy loss to electron hole pairs is the dominant energy dissipation pathway. Molecular dynamics simulations including nonadiabatic effects for multiple incidence conditions are in very good agreement with experiment. Furthermore, the theory offers an explanation for the apparent lack of an isotope effect observed experimentally. I consider the effect of changes in the electron density and the inclusion of surface reconstruction and find the results are not much altered. For molecular dynamics simulations and fitting, I used a self written program package to which I contributed substantially.