Electronic Structure and Bonding of Icosahedral Core-Shell Gold-Silver Nanoalloy Clusters Au144-xAgx(SR)60

Atomically precise thiolate-stabilized gold nanoclusters are currently of interest for many cross-disciplinary applications in chemistry, physics, and molecular biology. Very recently, synthesis and electronic properties of "nanoalloy" clusters Au144-xAgx(SR)(60) were reported. Here density functional theory is used for electronic structure and bonding in Au144-xAgx(SR)(60) based on a structural model of the icosahedral Au-144(SR)(60) that features a 114-atom metal core with 60 symmetry-equivalent surface sites and a protecting layer of 30 RSAuSR units. In the optimal configuration the 60 surface sites of the core are occupied by silver in Au84Ag60(SR)(60). Silver enhances the electron shell structure around the Fermi level in the metal core, which predicts a structured absorption spectrum around the onset (similar to 0.8 eV) of electronic metal-to-metal transitions. The calculations also imply element-dependent absorption edges for Au(5d) -> Au(6sp) and Ag(4d) -> Ag(5sp) interband transitions in the "plasmonic" region, with their relative intensities controlled by the Ag/Au mixing ratio.