MD simulation of water at imperfect platinum surfaces .1. Structure

The aim of our work was to study the water structure at surfaces that contain imperfections. A series of molecular dynamics simulations of water at Pt(100) walls were performed while systematically introducing different types of imperfections onto the surface. Point dislocations, monoatomic steps, kink sites and rectangular terraces were considered. It was found that imperfections can lead to vacant surface sites and can loosen the rigid hydrogen bonded structure of the adsorbed water layer. A vacancy is filled with a water molecule, whereas on the step edges, the water molecules sit on top sites. Some of them point their dipole moment vector and one of the OH vectors towards the surface. This new water configuration provides a further possibility for hydrogen bonding between molecules on the step edge and at the step side. The majority of the water molecules at the step sides are also on top positions on the next row of Pt-atoms of the basal plane. However, a number of water molecules are adsorbed to Pt-atoms within the step. Around the corner of a terrace water molecules occupy top sites. A kink site on the surface is empty, but there is a water molecule immediately next to the site, built into the step. The kink is also surrounded by two other water molecules sitting on top positions of the basal plane. This unique configuration serves as a structural evidence explaining the well known fact, that kink sites act as starting points for adsorption and metal deposition processes. (C) 1997 Elsevier Science S.A.