The hydration structure of the lithium(l) ion has been studied by a combined quantum mechanical/molecular mechanical molecular dynamics (QM/MM-MD) method at the HF and B3LYP level of theory. Water molecules of both the first and the second hydration shell have been included in the QM treatment. The effect of differently sized QM regions is discussed. The structure obtained by B3LYP is quite insensitive to changes in QM size whereas the HF simulation predicts a weak second hydration shell structure with a large QM region. (C) 2003 Elsevier B.V. All rights reserved.