An improvement of the macroscopic compressibility approximation

The Barker–Henderson macroscopic compressibility (mc) approximation of the second-order perturbation term is improved by assuming that the numbers of molecules in every two neighbouring shells are correlated, based upon their original assumptions. The results are better than those of the original mc and the local compressibility (lc) approximation, especially at intermediate and high densities, compared with simulation data for F2/(NkT).