A first principles theoretical study of the hydration structure and dynamics of an excess proton in water clusters of varying size and temperature

We present a theoretical study of the structure and dynamics of protonated water clusters by means of quantum chemical calculations and ab initio molecular dynamics simulations. We have considered the clusters H+(H2O)(n) for four different sizes corresponding to n = 5, 9, 17 and 21. We have first looked at the solvation states of the excess proton in several lower energy structures of these clusters with a special interest in finding its surface versus interior states and its hydrogen bonding environment. Subsequently, we have investigated the finite temperature behavior of these clusters through ab initio simulations. We have looked at vibrational spectral features with special emphasis given to the spectral features of free OH (deuterated) modes and their dependence on donor-acceptor hydrogen bonding states of the water molecules. We have also investigated the mechanism and kinetics of proton transfer events in these clusters by using a population correlation function approach. (C) 2011 Elsevier B.V. All rights reserved.