  Effective interactions between like-charged particles immersed in an
electrolyte solution were calculated using two integral equation theories,
hypernetted-chain (HNC)-Ornstein--Zernike (OZ) and ionic Percus--Yevick 2
(IPY2)-OZ. When the HNC-OZ theory was adopted, the electrolyte concentration
dependence of the effective interaction showed a reentrant behavior. By
contrast, the IPY2-OZ theory did not indicate the behavior. Monte Carlo
simulations were performed for one of the model systems, and the results agreed
qualitatively with those calculated using the HNC-OZ theory.
