A quantum self-consistent-charge density-functional tight-binding method was combined with a classical MM approach using GROMOS. The resulting integrated QM/MM model was applied in studies of dynamical properties of a quantum water molecule and a malonaldehyde molecule in classical water environment. Interactions between classical and quantum subsystems are described by electrostatic and van der Waals potential energy functions. Basic properties of water such as self-diffusion constant, a radial distribution function and infrared spectra were computed and compared with available experimental data. The model has also been successfully applied to intra-molecular proton transfer reaction in malonaldehyde in water solution. (C) 2004 Elsevier B.V. All rights reserved.