Mercury adsorption on small neutral and charged Ag(n) clusters has been investigated by using DFT method. The results show that frontier molecular orbital theory is a useful tool to predict the selectivity of Hg adsorption. The binding energies of Hg on the cations are generally greater than those on the corresponding neutral and anionic clusters. NBO analysis indicates the electron flow in the neutral and charged complexes is mainly from the s orbital of Ag to the s orbital of Hg. For neutral and anionic complexes, electron transfer also occurs from p orbital of Hg to s orbital of Ag. (C) 2011 Elsevier B.V. All rights reserved.