Effective interactions between like-charged macromolecules

We investigate, within a local density functional theory formalism, the int eractions between like-charged polyions immersed in a confined electrolyte. We obtain a simple condition for a repulsive effective pair potential, whi ch can be related to the thermodynamic stability criterion of the uncharged counterpart of microscopic species constituting the electrolyte. Under the same condition, the phenomenon of charge inversion (over-charging), where the polyion bare charge is over-screened by its electric double layer, is s hown to be impossible. These results hold beyond standard mean-field theori es (such as Poisson-Boltzmann or modified Poisson-Boltzmann approaches).