Ab initio study of the energetics of ionic hydration with the polarizable continuum model

Although they are computationally very demanding, quantum mechanical (ab initio) models provide the first step in the hierarchical ladder leading to the full computational description of matter. The formulation of an economic ab initio model of ionic hydration is reviewed here from the viewpoint of thermodynamics, statistical mechanics, and quantum mechanics. This manuscript presents an exposition of the polarizable continuum model (PCM), which encompasses the exact quantum mechanical problem for the solute, coupled with an electrostatic problem for the solvent, which is modeled as a uniform dielectric medium contained outside a cavity surrounding each ion. By the judicious choice of the scaled ionic radius, a single parameter that is intrinsic to each ion, PCM can reproduce the experimental values of the solvation energy of single monovalent cations and anions available in the literature. After a discussion of advantages and disadvantages of PCM, it is concluded that such quantum-continuum models can be easily refined in a self-consistent fashion and employed in the study of energetics and structure of systems of hydrated ions by researchers interested in nanoscale transport phenomena in liquids.