The first-order correction term for the contribution of dispersion forces i
n a perturbation expansion has been analyzed using computer simulation and
perturbation theory results. It turns out that simple approximations used t
o make an analytic evaluation of the correction integral possible may resul
t, ironically, in more complicated (and erroneous) behavior in comparison w
ith the exact result. (C) 2001 Elsevier Science B.V, All rights reserved.