Interaction of Au(16) Nanocluster with Defects in Supporting Graphite: A Density-Functional Study

Soft-landed adsorption of Au-16 on bilayered graphene is investigated using density functional theory. The orientation of the Au-16 cluster and number of neighboring surface vacancies affect the overall structural and electronic properties of the cluster. The results of the PBE, vdW-DF, and vdW-DF2 exchange-correlation functionals are compared for the cluster-substrate interaction for systems with and without defects. In the presence of defects size two and greater, an Au atom adsorbs into the topmost graphene layer; this strongly influences the binding energy (>3 eV), while inducing substantial bending in the carbon plane and altering electronic properties of the system. Though the T-d-symmetry and electronegative properties of the Au-16 structure change in the presence of greater neighboring defects, elements of the cagelike starting structure remain throughout. The electron localization function shows that the in-plane Au-C bonds are of delocalized (metallic) nature and there is a local charge transfer to the coordinating Au. However, the net charge transfer between adsorbate and substrate is considerable only for the defect-free case (0.8e to Au-16). Finally, the binding of O-2 molecules to the adsorbed Au-16 cluster is used to probe the potential catalytic activity of graphite and carbon nanotube systems, and in one case (for defect size two) the adsorbed O-2 switches on the catalytically active superoxo-state