We have studied the adsorption of a number of organic molecules consisting of methyl, benzyl, and carboxylic groups on the rutile TiO2 (110) surface using both ab initio and atomistic simulation techniques. We have tested the applicability of a simple embedded cluster model to studying the adsorption of small organic molecules on the perfect rutile TiO2 (110) surface, and used this model to develop a classical force field for the interactions of a wide class of organic molecules consisting of these groups with the rutile TiO2 (110) surface. The force field accounts for physisorption and ionic bonding of organic molecules at the surface. It allows the reproduction of adsorption energies and of geometries of organic molecules on the rutile surface. It should be useful for studying diffusion of these molecules and their manipulation with use of AFM and STM tips.