Structural and dynamical characteristics of mesoscopic H$^+$[H$_2$O]$_n$ clusters

Structural and dynamical characteristics pertaining to the solvation of an excess proton in liquid-like nanoclusters of the type [H$_2$O]$_n$ are investigated using Molecular Dynamics experiments. Three different aggregate sizes were analyzed: $n=10,$ 21 and 125. The simulation experiments were performed using a multistate empirical valence bond Hamiltonian model. While in the smallest aggregates the proton occupies a central position, the stable solvation environments for $n=21$ and 125 are located at the cluster boundaries. In all cases, the structure of the closest solvation shell of the excess charge remains practically unchanged and coincides with that observed in bulk water. Compared to results obtained in bulk, the computed rates for proton transfer in clusters are between one and two orders of magnitude slower, and tend to increase for larger cluster sizes.
Comment: 16 pages, 6 figures, to be published in Journal of Molecular Liquids, EMLG2006 special issue