Intrinsic disorder of dangling OH-bonds in the first water layer on noble metal surfaces

Using the first-principles calculation, we have systematically investigated the orientation of dangling OH-bonds in the first adsorbed water layer on close packed surface of noble metals (gold, platinum and palladium). We find that, the distribution of up and down dangling OH-bonds can strongly change the adsorption stability. A specific distribution of dangling OH-bonds is always indispensable in various adsorption patterns for its stability. The in-plane arrangement of water molecules also has important influence on the orientation of dangling OH-bonds. More importantly, the disorder in the orientation (up or down) of dangling OH manifests a kind of zero-temperature residual entropy in some absorption structures. In essence, the residual entropy arises from the competition between water-water and water-metal interactions, which is different from the counterpart in ice crystals.