PROTON SOLVATION IN LIQUID WATER - AN ABINITIO 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 hyd ronium ion has been selected as the starting point for all our calcula tions. The ion and the ion plus a first solvation shell have been used as solutes in the continuum calculations, and the results have been c ompared with a discrete model with two explicit solvation shells. Acco rding to various experimental studies, we have found a well-defined fi rst solvation shell with three water molecules, while the preferred lo cation of a fourth water molecule is in the second shell, both in the gas phase and in solution. Although the combined discrete-continuum mo del gives an energy value in good agreement with experiment, some defi ciencies, related to the noninclusion of charge transfer beyond the ca vity, have been found.