Representing an Infinite Solvent System with a Rectangular Finite System Using Image Charges

Abstract

We have developed a novel solvent boundary potential for nonspherical charged systems based on a Rectangular Image Charge (RIC) method. This method is similar to the Kirkwood theory in that both methods solve for the potential in one dielectric cavity immersed in another dielectric material. The key difference is that the RIC method employs rectangular coordinates as opposed to spherical coordinates in the Kirkwood theory and hence can be applied to nonspherical systems. The RIC method yields electrostatic reaction fields and energies in accord with those obtained by numerical solution to a Poisson equation. It also yields accurate cation−water oxygen radial distribution functions as well as absolute free energies. Furthermore, the absolute free energy of an ion was verified to be independent of its location in the cubic box, indicating that the present method can extend the finite cubic system into an infinite solvent system.