where EPt is the total energy of the bare surface, EH 2 O is the total energy of the water molecule, E Pt-H 2 O is the total energy of the bilayer adsorbed surface system, and n is the number of water molecules in the unit cell. The calculated adsorption energies are given in Figure (blue panel). Including van der Waals interaction significantly improves the adsorption energies of water bilayers over the surface. Both water bilayers and monomers follow a similar trend in adsorption strength across the functionals considered. Hence, the trends in the prediction of metal-H2O interaction strength by these methods can be considered to be not affected by the coverage of H2O molecules. Bilayer interaction with the metal surface is a cumulative effect of both metal-water and waterwater interactions. Hence, in order to decouple these interactions, we have calculated the hydrogen bonding energy as;