To improve the accuracy and transferability of molecular mechanics force fields, one needs a simple physical description of intermolecular polarization based on quantum chemistry. Ideally, in the quantum-chemical description, each molecule is treated separately and the interactions with other molecules are included as a perturbation. We propose a simple formulation of this perturbation, viz. to model the electrostatic part of the interactions exactly and the repulsive counterpart by a two-parameter pseudo-potential. Tests on three dimers at the Hartree-Fock and MP2 levels show that the interaction energies and the polarized charge densities are well reproduced. (C) 2008 Elsevier B. V. All rights reserved.