Proton solvation in liquid water. An ab initio study using the continuum model

The proton solvation process is studied by means of a continuum model using a quantum description of the solute charge distribution. The hydronium ion has been selected as the starting point for all our calculations. The ion and the ion plus a first solvation shell have been used as solutes in the continuum calculations, and the results have been compared with a discrete model with two explicit solvation shells. According to various experimental studies, we have found a well-defined first solvation shell with three water molecules, while the preferred location of a fourth water molecule is in the second shell, both in the gas phase and in solution. Although the combined discrete-continuum model gives an energy value in good agreement with experiment, some deficiencies, related to the noninclusion of charge transfer beyond the cavity, have been found. © 1993 American Chemical Society.