Classical and ab initio QM/MM molecular dynamics simulations have been performed for Hg2+ in aqueous solution. The dynamical properties were evaluated in terms of librational and vibrational motions of water molecules in the first and second hydration shell. The frequencies of rotation of water molecules in the first shell are blue-shifted compared to those of pure liquid water. Water exchange between first and second hydration shell occurs with a mean ligand residence time of 87 ps, in good agreement with the experimentally estimated value. (C) 2003 Elsevier Science B.V. All rights reserved.