Electronic structure and photochemical properties of a monolayer-protected gold cluster

The electronic structure of a monolayer-protected gold cluster, [Au-13(SCH3)(8)](3+), has been investigated by performing density functional calculations. The cluster has a characteristic structure with O-h molecular symmetry, and eight (111) facets of a centered cuboctahedral Au-13 core cluster are fully passivated by eight methanethiolates. The bond distance between two neighboring gold atoms (3.673 Angstrom) is much larger than that of the bare Au-13 cluster (2.929 Angstrom), whereas the Au-S bond distance is 2.403 Angstrom. This atomic rearrangement means that the methanethiolates stabilize the enlarged bare An 13 cluster by bonding to the (111) hollow sites of the bare cluster. The absorption spectrum of the [Au-13(SCH3)(8)](3+) cluster is simulated within time-dependent density functional theory. The spectrum shows clear absorption peaks and each peak is assigned to specific excitation processes.