Theoretical study for water structure at highly ordered surface: Effect of surface structure

The structure of water at an ordered solid surface is investigated by the reference interaction site method (RISM). A RISM equation devised especially for a solute-solvent system in which the solute is a two-dimensional periodic array is employed to formulate the electrode-solution interface. Calculations are carried out for two types of surfaces: hatlike and Au(111)-like structures. The orientation of water molecules at the Au(111)-like surface with various surface charge densities, which are deduced from the correlation functions, is in good agreement with the results of surface-enhanced infrared absorption spectroscopy. On the other hand, the model of the flatlike surface does not give a consistent picture with the experiments. The difference is significant when the walls are negatively charged. In the case of a negatively charged wall, the Au(111)-like model gives about 108 degrees for the angle between the surface normal vector and the two O-H vectors of the water molecules in the first layer, whereas the angles are about 72 degrees and 180 degrees for the Batlike surface. The results demonstrate that the solid surface structure is very important in discussing the structure and orientation of water molecules at the interface. (C) 1998 American Institute of Physics.