A stable local density functional approach to ion-ion correlations
Instituto de Física, Universidade Federal do Rio
Grande do Sul Caixa Postal 15051, 91501-970 Porto Alegre
2 Max-Planck-Institut für Polymerforschung Ackermannweg 10, 55128 Mainz, Germany
Accepted: 2 August 2000
We propose a new approach for incorporating counterion correlations into Poisson-Boltzmann–like theories, which is based on a local density functional for the system of counterions. Our derivation is inspired by the Debye-Hückel approach to the one-component plasma (OCP). An artificial instability due to the OCP's homogeneous background charge —which is absent in the original counterion system— is overcome by excluding the background from the vicinity of a central ion. The resulting free energy density is convex and thus applicable within a local density approximation. For the simple example of a strongly charged stiff rod surrounded by its counterions we demonstrate that the Poisson-Boltzmann free energy functional augmented by our new correction accounts for the correlations present in this system when compared to molecular dynamics simulations.
PACS: 61.20.Qg – Structure of associated liquids: electrolytes, molten salts, etc / 82.70.-y – Disperse systems / 05.70.Ce – Thermodynamic functions and equations of state
© EDP Sciences, 2000