The ground-state structure, optical-absorption and photoelectron spectrum of silver clusters

The most stable structure, optical-absorption and photoelectron spectrum of neutral and anionic silver clusters up to 16 atoms have been studied by using particle-swarm optimization technique and density functional theory (DFT). A comprehensive structural search was carried out and many isomers were obtained. The ground state structures of neutral silver clusters have been determined by optical absorption spectrum and vertical ionization potential (VIP). Starting from n = 11, the growth of Ag-n clusters follows a regular pattern. The infrared and Raman spectra of neutral silver clusters are predicted and can be used to identify these structures from experiments. The experimental photoelectron spectra (PES) of silver cluster anion are interpreted reasonably for the first time. Meantime, we find that the peak height of the measured PES in the range of binding energy close to the photon energy decreases significantly relative to the theoretical height. The reduction may be due to the small kinetic energy of photoelectron.