The benzene-water system is a model for understanding the interactions within bio-molecules. We performed a series of molecular dynamics simulations with hybrid QM/MM potentials, where benzene and one of the water molecules were treated quantum mechanically, while other waters were treated by molecular mechanics. The umbrella sampling method was employed to realize effective sampling and the potential of mean force (PMF) was obtained for water associated with benzene using the weighted histogram analysis method. The resulting PMF was then compared with that derived by a conventional molecular mechanics method and was found to be in accord with the experimental result. (c) 2006 Elsevier B.V. All rights reserved.