  We investigate the shifts of the core-level binding energies in small gold
nanoclusters by using {\it ab initio} density functional theory calculations.
The shift of the 4$f$ states is calculated for magic number nanoclusters in a
wide range of sizes and morphologies. We find a non-monotonous behavior of the
core-level shift in nanoclusters depending on the size. We demonstrate that
there are three main contributions to the Au 4$f$ 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.
