On the possibility of obtaining an effective pairwise additive intermolecular pontential via an ab-initio route by fitting to a cooperative model of condensed phase configurations Abstract: The paper demonstrates the feasibility of obtaining an effective pairwise additive intermolecular potential for liquid water at room temperature by fitting a pairwise additive function to the cooperatively calculated energies and virial sums of simulated liquid water configurations. The procedure requires iterative refinement of the fit. The importance of trying different functional forms has been demonstrated as well as the importance of including the virial sum into the fitting process. The cooperative energies and virial sums were calculated with the Campbell-Mezei model (derived from ab initio dimer energies) that includes a dipole polarization term.