In search of a structural model for a thiolate-protected Au38 cluster

The structure of thiolate-protected gold cluster Au-38(SR)(24) has not been experimentally determined, and the best available signature is its measured optical spectrum. Using this signature and energetic stability as criteria and SCH3 for SR, we compare four candidate structures: two from others and two we obtained. Our models are distinct from others' in that thiolate groups form monomers and dimers of the staple motif (a nearly linear RS-Au-SR bonding unit). We examine the energetics and electronic structures of the four structures with density functional theory (DFT) and compute their optical spectra with time-dependent DFT. We show that our dimer-dominated model is over 2.6 eV lower in energy than the two models from others and 1.3 eV lower than our previous monomer-dominated model. The dimer-dominated model also presents good agreement with experiment for optical absorption.