The structure of water on the (0 0 0 1) surface of graphite

The structure of water layers on the close-packed surface of graphite has been studied using electronic structure total energy computations. At all coverages, the water molecules are found to be only physisorbed, lying at least 3.5 إ above the graphite and showing no bonding interactions evidenced in electronic orbitals or total electron density. At low coverages, the water shows little preference for orientation or surface site. Increasing coverage by reducing the size of the unit cell leads to a preference for orientation of molecules such that the dipole is parallel to the surface. This is shown to arise from the electrostatic interaction of molecules with their own periodic images. The structures of small water clusters are found to agree with those determined for free, gas-phase clusters. Further increases of coverage lead to the formation of extended ice-like layers.