Studies in Molecular Dynamics. X. Corrections to the Augmented van der Waals Theory for the Square Well Fluid

The validity of the augmented van der Waals theory of fluids is demonstrated by a rigorous evaluation of the next three terms in the reciprocal temperature expansion of the Helmholtz free energy for the square‐well fluid. Each term in the dense fluid is shown to be an order of magnitude smaller than the preceding one except the fourth, which is comparable to the third. Analysis of molecular dynamics data leads to a peak in the heat capacity at the coexistence curve which is not reproduced by the finite series. This peak in turn leads to realistic values of the critical indices α and $\mathrm{\alpha \prime }$ while the other indices β, γ, and δ have their classical van der Waals values.