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.