Density functional study of gold atoms and clusters on a graphite (0001) surface with defects

Adsorption of gold atoms and clusters (N=6) on a graphite (0001) surface with defects has been studied using density functional theory. In addition to perfect graphite (0001), three types of surface defects have been considered: a surface vacancy (hole), a pyridinelike defect comprising three grouped nitrogen atoms, and a substitutional doping by N or B. Results for Au and Au-6 indicate that the surface vacancy can form chemical bonds with Au as the three nearby carbons align their dangling bonds towards the gold particle (binding energy 2.4-2.6 eV). A similar chemically saturated holelike construction with three pyridinic N atoms results in a significant polarization interaction (1.1-1.2 eV), whereas the binding with the perfect graphite surface is weak (similar to 0.3 eV). The corresponding energies for the B/N substituted surface are 0.8-1.2 eV (B) and 0.2-0.6 eV (N), and the N impurity donates charge to Au/Au-6. Several Au-6 isomers have been tested in different orientations on substrate, and the triangular gas-phase geometry (D-3h) standing on its apex is a low-energy configuration (N substitution is an exception). In general, coordination through corner atoms is energetically favorable. For the surface vacancy, the presence of gold particles leads to a significant surface reconstruction, whereas the pyridinelike defect appears rigid. There is no significant charge transfer, and the net charge on Au-6 ranges between -0.2e and 0.1e