Structure of Hydrated $\alpha$-Fe$_2$O$_3$ (0001) and (1$\bar{1}$02)*

The structure and reactivity of $\alpha$-Fe$_2$O$_3$ depends on several factors, including the composition of the bulk material, crystallographic orientation, and local coordination of the surface atoms. As an example, the adsorption and dissociation of water on $\alpha$-Fe$_2$O$_3$ and other metal oxide surfaces is not well understood, since the oxide surface has largely been characterized under ultrahigh vacuum or clean conditions. However, interactions at the solid-liquid and solid-solid interface play major roles in environmental processes, including contaminant sequestration, mobility, and bioavailability. In this work, we present density functional theory results on the structure of clean and hydrated $\alpha$-Fe$_2$O$_3$ (0001) and (1$\bar{1}$02), and show the changes in surface structure upon heterolytic water dissociation and water physisorption.