Paper SS2+NC-ThM12
Ligand-Spacer Controlled Size Selectivity of Gold Nanoclusters and the Effect of the Ligand on Cluster Geometry and Electronic Structure

Thursday, October 23, 2008, 11:40 am, Room 208

We have carried¹ out calculations based on the density functional theory in the projector augmented wave scheme (PAW) and the pseudopotential approach, to examine the effect of the size of the diphosphine ligand spacers on the stability of Au clusters containing 8 and 11 atoms, through evaluations of the cluster total energy and proper correction of spurious interactions between charged supercells. We find that Au11+3 is indeed preferred by ligand L3 rather than L5, while Au8+5 is preferred by L5 rather than L3, in agreement with experimental data.² The size selectivity induced by the ligand is found to be a purely electronic effect via coupling of the d-band of Au and p-band of the ligand. We have also examined the effect of the ligand on the geometric and electronic structure of Au clusters. For Au13, for example, we find bare cluster to form a flat flake, in agreement with previous theoretical calculations. On the other hand, Au13 cluster covered with ligands of phosphine (PH3) forms a stable spherical structure (icosahedron), in agreement with experimental findings,² which is 0.08 eV lower in energy as compared to the flat-flake complex. If the phosphine is replaced by H, the spherical structure is no longer stable, but it still maintains a 3 dimensional form, signifying the effect of the ligand in stabilization of the structure. We observe a narrow d-band for gold atoms in the flat-flake complex, while in the icosahedron structure the d-band is wider. We also find a stronger overlap between the p orbitals of the P atom with d orbitals of gold atoms in the icosahedron complex.

¹ Work supported in part by by NSF Grant CHE-0741423.
² M. Bertino et al. Jour. Phys. Chem. B Lett. 110, 21416 (2006).