  Effective attraction between like-charged walls mediated by counterions is
studied using local molecular field (LMF) theory. Monte Carlo simulations of
the "mimic system'' given by LMF theory, with short-ranged "Coulomb core"
interactions in an effective single particle potential incorporating a
mean-field average of the long-ranged Coulomb interactions, provide a direct
test of the theory, and are in excellent agreement with more complex
simulations of the full Coulomb system by Moreira and Netz [Eur. Phys. J. E 8,
33 (2002)]. A simple, generally-applicable criterion to determine the
consistency parameter sigma_{min} needed for accurate use of the LMF theory is
presented.
