First principles study of the Ga(10$\bar{1}$0)/water interface

Pure GaN is a water-splitting photocatalyst which works in UV light. A first-principles study shows monolayer of water molecules on the (10$\bar{1}$0) surface of wurtzite GaN have negligible barrier to be dissociated into OH$^-$ which bind to Ga$^+$ and H$^+$ which bind to N$^-$.\footnote{X.Shen {\it et al.}, J. Phys. Chem. C {\bf 113}, 3365 (2009)} We present an \textit{ab initio} molecule dynamics study of bulk water molecules on top of the (10$\bar{1}$0) surface of GaN. The dissociation of water molecules happens very fast within the first ps of simulation. We find that OH$^{-}\cdot\cdot\cdot$ OH$^-$ Hydrogen bond are formed between two OH$^{-}$ on the surface. We propose two different types of OH$^{-}$ based on the different H-bond structure between them and the bulk water molecules. We also calculate the vibrational spectrum and the interface electronic structure of the semiconductor/aqueous system.