A MODIFIED SUPERPOSITION APPROXIMATION TO THE 3-BODY DISTRIBUTION FUNCTION

Based on quite general arguments we propose a simple modification to the Kirkwood superposition approximation. It consists in the replacement of g2(r) by alpha(r)g2[alpha(r)r] with alpha(r) = 1 + gamma/r. This modification is tested against numerical simulations of a Lennard-Jones fluid, and good results are obtained. The gamma value seems to be quite independent of the thermodynamic parameters of the system and of the precise functional form of a. Based on short-range universality arguments, we propose gamma = 0.07 for all simple fluids.