Density-functional theory for attraction between like-charged plates

We study the interactions between two negatively charged macroscopic surfac es confining positive counterions. A density-functional approach is introdu ced which, besides the usual mean-field interactions, takes into account th e correlations in the positions of counterions. The excess free energy is d erived in the framework of the Debye-Huckel theory of the one-component pla sma, with the homogeneous density replaced by a weighted density. The minim ization of the total free energy yields the density profile of the microion s. The pressure is calculated and compared with the simulations and the res ults derived from integral equations theories. We find that the interaction between the two plates becomes attractive when their separation distance i s sufficiently small and the surface charge density is larger than a thresh old value. (C) 1999 Elsevier Science B.V. All rights reserved.