Reaction path for dissociative water adsorption on vicinal anatase (101) surface*

Using density functional calculations and a periodical slab model, we investigate water adsorption on edges formed by intersection of two anatase TiO$_2$ (101) surfaces. We find that after adsorption of a water molecule on a low-coordinated Ti atom on the ridge, decomposition may happen over a moderatly high barrier. In this process, a proton gets abstracted by bonding to a low-coodinated ridge oxygen atom. The hydroxyl anion remains bonded to the acidic Ti site on the edge. The methods used to find the saddle points and to map out the reaction paths are briefly discussed. We also give a discussion of the reaction rates that may be expected based on these calculations. The presence of hydroxyl groups and protons is favoring nucleation of Ca phoshate bonding by allowing exchange of the adsorbed proton against Ca$^{2+}$ ions. Such processes are thought to be essential for the biocompatibility of titanium and its use in dental and orthopedic applications.