The ground-state bonding of water on alkali metal bcc(100) surfaces: A contrasting model to H2O/Pt systems

Our knowledge of water bonding on metal surfaces is largely limited to the conventional picture, which highlights the well-known flat-on-top configurations as the general bonding geometry. By using density functional theory calculations, here we report that the conventional picture needs to be significantly modified when water goes to alkali bcc(100) metal surfaces, which leads to the unique ground-state configurations preferentially occupying the bridge sites. We have discovered that the occupied and unoccupied molecular orbitals play fundamentally different roles in the water-metal bonds, in sharp contrast to the conventional picture of water on transition metal surfaces. The occupied molecular orbitals are localized with the molecule and exert pure electrostatics in water-metal interactions, whereas the unoccupied molecular orbitals become completely delocalized and exert observable covalent contributions. The new picture not only geometrically but also electronically advances our understanding of how water makes bonds with metal surfaces.