Wetting of Intact and Partially Dissociated Water Layer on Ru(0001): a Density Functional Study

Factors that influence the multilayered wetting of Ru surface are discussed by use of density functional theory calculations of adsorption of bilayers of water on Ru(0001), comparing addition of intact bilayers to a first one containing partially dissociated or intact water molecules. For the first bilayer on Ru(0001), we find that a partial dissociation of 3/8 of the water molecules is slightly more stable than the half-dissociation; this bilayer contains H-up water molecules pointing up to the vacuum, allowing further adsorption. We show that wetting of the first water layer on Ru(0001) is more favorable for the partially dissociated structures than for the intact one. For two intact water bilayers that are almost planar, there is no hydrogen available to adsorb a third bilayer, which agrees with the experimental results showing unstable ice films on adsorbed intact-water bilayer. We found that the most stable structures of two bilayers on Ru(0001) are those in which 3/8 of the water molecules from the first bilayer are dissociated. This structure has hydrogen atoms pointing to the top, suggesting its ability to adsorb a third layer. The structures with 1/4 partially dissociated first bilayer are close in energy, while structures with half-dissociated first layer are less stable.