Atomic scale characterization of interfacial water near an oxide surface using molecular dynamics simulations

Abstract

Atomic scale characterization of the structure and dynamics of confined water molecules located near the metal oxide–aqueous interface is carried out using molecular dynamics simulations. Proximity effects on water molecules (H₂O) near a magnesium oxide surface (MgO(100)) at room temperature are evaluated based on various structural and dynamical correlation functions. Translational and orientational order parameters are used to quantify the extent of ordering of water molecules near the oxide surface. There is significant ordering of water molecules in the two layers close to the oxide interface and the extent of ordering decreases with increasing distance from the oxide–water interface. The characteristic structural features of proximal water molecules near oxide–aqueous interfaces are strongly correlated to their vibrational densities of states. Systematic trends in libration, bending, and stretching bands are correlated with local ordering of water molecules and the hydrogen-bonding network. We find that restricted transverse oscillations result in larger blue shifts in O–O–O bending and O–O stretching bands for water molecules having increased proximity to the interface. The O–H stretching band is red-shifted whereas the libration bands for proximal water are blue shifted with respect to bulk water; the extent of shifts are sensitive to the interface proximity, their local confinement and their hydrogen bonding status.