Analytic radial distribution function for square-well plus Van der Waals potential

In classical statistical mechanics, and under the assumption of pairwise additivity of intermolecular forces, the term g1( r,T), which is the coefficient of the linear density in the expansion of the radial distribution function in powers of the density, has been evaluated in the case of square-well plus Van der Waals potential. The square well used has a depth epsilon, a hard-core diameter sigma and an attractive diameter lambda sigma, where lambda (<=)3. For lambda =1, an up to term in βsup(2) (β=1/KT), the result reduces to that for the Sutherland (infinity, 6) potential obtained by Chen, but with an additional term for r(>=)2sigma and another for r(<=)2sigma, which are consequences of expanding Mayer's f-function for the Van der Waals part up to the term in βsup(2). By annulling the Van der Waals part, and for lambda=2, the result reduces to that given by McQuarrie for the square-well potential with an attractive diameter 2sigma