A self-consistent local-density scheme is used to compute the polarizability of rare-gas atoms in the liquid phase at the triple point. First-principles total-energy calculations are performed for the crystal, and Lennard-Jones parameters for interatomic potentials are deduced which are in reasonable agreement with empirical values. Hence, the environmental potential in the liquid is constructed with use of existing molecular-dynamics results for the pair correlation function of a Lennard-Jones fluid. It is suggested that such calculations provide an additional way of assessing effective pair potentials.