Computational x-ray absorption spectroscopy of gold nanoclusters.

Gold nanoclusters (NCs) are tiny molecules with a gold core protected by an organic ligand layer. They possess a wide range of applications, facilitated by their designability at the atomistic level. They are used in catalysis, bioimaging, biosensing, drug delivery, or as optical waveguides. X-ray absorption spectroscopy (XAS) can provide information about orbital specific density of states, oxidation states, core electron binding energies, and the bonding types occurring in molecules and nanoclusters. Interpreting these data at a single atom level needs a detailed and trustworthy approach to simulate the XAS properties of NCs atom by atom. Here, we investigate L-edge x-ray absorption near edge spectroscopy for various ligand-protected gold NCs (Au13, Au22, Au44, Au102, and Au144) protected by chemically diverse ligand molecules and interpret details of their electronic structure. We show that XAS properties of gold atoms inside these clusters are very diverse depending on their chemical environment and symmetry. Our work deepens the understanding of spatial variations of local oxidation states, charge distributions, and chemical bonding environments of gold atoms inside ligand-protected clusters, highlighting the impact of diverse ligand environments.