Water Kinetics and Clustering on the (101) TiO2 Anatase Surface

(101) anatase TiO2 surface in water ambient is an important system for the interaction of biocompatible nanodevices with biological environment. Following the experimental evidence showing that water molecules are mobile at temperature as low as 190 K and tend to form clusters along the [11 (1) over bar]/[1 (11) over bar] surface directions, a complete theoretical characterization of the dynamical properties of the first water layer on the (101) anatase TiO2 surface is presented. A variety of computational techniques have been employed in the context of the transition-state theory in the harmonic regime, ranging from first-principles total energy ground-state calculations, to density functional perturbation theory, minimum energy path search, and kinetic Monte Carlo simulations, to explain the experimental results on water kinetics on the (101) anatase TiO2 surface. We have calculated the migration energy barrier of water molecules, the vibrational prefactor through the phonon density of states, and the hopping rate along two principal directions. Lastly, in a kinetic Monte Carlo context, we have simulated and clarified the dynamical processes that are on the basis of the observed experimental behavior.