Ti-O bond distance fluctuations at the hydrated rutile (110) surface

We studied water on the rutile (110) surface using ab-initio molecular dynamics simulations in NVT ensemble at 280K, 300K, and 320K. Water adsorbs on the 5-fold coordinated titanium atoms or dissociates transferring a proton to a bridging-oxygen atom. The equilibrium between these configurations is dynamical and depends on temperature and water coverage. The titanium-oxygen bond distances at the surface can change as much as 12{\%} depending on the number of hydrogen atoms bonded to oxygen. Hydrogen bonds also affect this distance. A measurement of the Ti-O distance at the surface can be used to estimate the average degree of dissociation. In view of our simulation results, the experimental evidence, such as photoelectron diffraction, indicates a low degree of dissociation under dry conditions.