Atomistic simulation of adsorption of water on three-, four- and five-coordinated surface sites of magnesium oxide

Physisorption of water molecules on three-, four- and five-coordinated surface sites of MgO, modelled by the {100}, {310} and facetted {111} surfaces, has been studied using atomistic simulation techniques. It was found that physisorption is energetically favourable on all three different surface sites, but that it is most advantageous on the lower-coordinated sites, in agreement with experiment. However, it was found that coordination of the physisorbed water molecule to hydroxylated species stabilises physisorption of the five-coordinated surface sites. Intermolecular interactions between the physisorbed water molecules stabilise or destabilise the adsorbed layer, depending on geometry, but this effect is outweighed by the formation of a strong electrostatic interaction between the surface Mg ion and water oxygen ion.