Integral equation for the structure of fluids in presence of three-body forces: Krypton, argon, and models for complex mixtures

The modified hypernetted chain and the crossover integral equations for the radial distribution function are generalized to take into account three-body forces. Good agreement with the simulation results is found. The structure factor and its isothermal density derivative for krypton and argon are computed with a realistic two-body potential plus the Axilrod–Teller three-body interaction. For krypton at medium density a very good agreement with experiment if found. At higher densities we find significant deviations both for krypton and for argon. The effect of three-body forces becomes very significant when the two-body potential has a narrow attractive well as it is the case in micellar solutions or microemulsions. In particular the critical point can be shifted to a very low value of concentration and there is enhancement of concentration fluctuations for a given value of the correlation length.