Abstract:

A molecular model for the water/platinum interface has been devised. It includes the surface corrugation of the metal and orientationally anisotropic water-metal interactions obtained from quantum chemical cluster calculations. Barriers for the surface diffusion and for the reorientation of a single water molecule on the quadratic (100) face of the face-centered-cubic platinum crystal are discussed. The flexible BoppJancs6-Heinzinger water model describes the water-water interactions, and the platinum-platinum interactions are described by a single force constant. Molecular dynamics simulations of a water lamina confined by (100) platinum surfaces have been performed using these interaction potentials. The structure is discussed on the basis of one-particle density profiles and solvent pair correlation functions. The surface-induced structural inhomogeneity ranges up to distances of IO A. In the center of the lamina water properties are bulklike. Hydrogen bonding in the vicinity of the interface is only slightly reduced relative to the bulk. The orientational structure of water is strongly influenced by water-water interactions and is considerably different from the preferential orientation according to the water-platinum interaction potential. It leads to a dipolar potential drop across the interface of 1.1 V.