On the importance of the first order blip expansion term in WCA-type perturbation theories

Abstract

Different perturbation theories of the Weeks—Chandler—Andersen (WCA) type are considered. In the Fischer—Lago—Bohn (FLB) theory, the first order term in the blip expansion is treated according to a suggestion of Perram. However, in the original Lee—Levesque (LL) theory as well as in the modification WCA—LL—GH the unlike blip term is neglected. It is shown that starting from FLB theory but neglecting the unlike blip term produces a version of perturbation theory that is unsatisfactory for large deviations from the Lorentz—Berthelot rules.