Ab initio studies of a water layer at transition metal surfaces

This paper presents a detailed study of a water adlayer adsorbed on Pt(111) and Rh(111) surfaces using periodic d. functional theory methods. The interaction between the metal surface and the water mols. is assessed from mol. dynamics simulation data and single point electronic structure calcns. of selected configurations. It is argued that the electron bands around the Fermi level of the metal substrate extend over the water adlayer. As a consequence in the presence of the water layer the surface as a whole still maintains its metallic cond.-a result of a crucial importance for understanding the process of electron transfer through the water/metal interface and electrochem. reactions in particular. Our results also indicate that there exists a weak bond between the hydrogen of the water and the Rh metal atoms as opposed to the widespread (classical) models based on purely repulsive interaction. This suggests that the commonly used classical interactions potentials adopted for large scale mol. dynamics simulations of water/metal interfaces may need revision. Two adsorption models of water on transition metals with the OH bonds pointing towards or away of the surface are also examd. It is shown that due to the very close values of their adsorption energies one should consider the real structure of water on the surface as a mixt. of these simple \ up\ and \ down\ models. A model for the structure of the adsorbed water layer on Rh(111) is proposed in terms of statistical avs. from mol. dynamics simulations. [on SciFinder (R)