Dynamic properties of hydrated aluminium(III) ion have been investigated by ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulations at Hartree-Fock level including only the first or first plus second hydration shell into the QM region. The octahedral Al-O frequencies and ligand exchange processes between second shell and bulk have been evaluated. The results show that quantum effects play a non-negligible role also in the interaction of first and second shell and that inclusion of the latter into the QM region improves the values of sensitive dynamical data. (c) 2006 Elsevier B.V. All rights reserved.