Origin of the core-level binding energy shifts in Au nanoclusters

We investigate the shifts of the core-level binding energies in small gold nanoclusters by using ab initio density-functional-theory calculations. The shift of the 4f states is calculated for magic-number nanoclusters in a wide range of sizes and morphologies. We find a nonmonotonous behavior of the core-level shift in nanoclusters depending on the size. We demonstrate that there are three main contributions to the Au 4f shifts, which depend sensitively on the interatomic distances, coordination, and quantum confinement. They are identified and explained by the change of the on-site electrostatic potential.