Charge separation in Coulomb liquids: mean-spherical approximation and Monte Carlo simulation

With reference to dense ionic liquids like the alkali metal-alkali halide melts, M-x[MX](1-x), we present a study of the distribution of the excess electronic charge x in Coulomb systems with electronic degrees of freedom. Within the mean-spherical approximation to the restricted primitive model of ionic liquids, we demonstrate the stability of systems that exhibit a maximum separation of cationic charges, z(M) is an element of {0,1}. The results are verified and illustrated by Monte Carlo simulations. We discuss the implications of the principle of maximum charge separation for the electronic structure and the thermodynamics of dense ionic liquids, possible additional applications and its limitations due to the neglect of quantum effects.