DFT-GGA and DFT+U Simulations of Thin Water Layers on Reduced TiO2 Anatase

We investigated the effect of a reducing subsurface Ti interstitial defect on the structure and reactivity of thin water layers adsorbed on the majority anatase(101) surface of titanium oxide using ab initio molecular dynamics simulations. We find that standard DFT-GGA and the DFT+U method predict similar energetics and dissociation barrier for a single water molecule adsorbed on the reduced surface; moreover, the two approaches also lead to very similar structural features and reactivity for an adsorbed water monolayer (ML) on the same surface. This allows us to model 1, 2, and 3 water layers on the reduced surface through Car-Parrinello molecular dynamics simulations up to 20 ps long. Compared to the defect-free surface, the simulations highlight how the interstitial defect alters the stability of surface adsorption sites, substantially enhancing the surface reactivity and leading to a markedly different structure of the first water layers adsorbed on the reduced surface.