Modeling thiolate-protected gold clusters with density-functional tight-binding

Thiolate-protected gold clusters are complex systems, in which both the surface-covalent Au-S bond and electronic structure of the gold core play an important role for the stability. In this study, a charge-self-consistent density-functional tight-binding parametrization for these systems is validated by studying Au-25(SMe)(-)(18), Au-102(SMe)(44) and Au-144(SMe)(60) clusters, where recent X-ray structure determinations and density-functional calculations have revealed the detailed atomic structures and electronic properties. We show that the cluster geometries obtained from the tight-binding structure relaxation preserve the Divide and Protect structure motif [H. Hakkinen, M. Walter, H. Gronbeck, J. Phys. Chem. B 110, 9927 (2006)], where the gold core is protected by a number of oligomeric Au-x(SR)(y) units. Furthermore, the electron shell structure in the metal core, composed of Au(6s) electrons, is reproduced. We conclude that the density-functional tight-binding method describes these systems well and offers a possibility to explore their dynamical phenomena.