6533b828fe1ef96bd1288f5d

RESEARCH PRODUCT

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

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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 ${\mathrm{Au}}_{6}$ 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--$2.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$). A similar chemically saturated holelike construction with three pyridinic N atoms results in a significant polarization interaction (1.1--$1.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$), whereas the binding with the perfect graphite surface is weak $(\ensuremath{\sim}0.3\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$. The corresponding energies for the $\mathrm{B}∕\mathrm{N}$ substituted surface are 0.8--$1.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (B) and 0.2--$0.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (N), and the N impurity donates charge to $\mathrm{Au}∕{\mathrm{Au}}_{6}$. Several ${\mathrm{Au}}_{6}$ 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 ${\mathrm{Au}}_{6}$ ranges between $\ensuremath{-}0.2e$ and $0.1e$.