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The results of ab initio molecular dynamics simulations of liquid water and liquid water–vapor interface using the Perdew-Wang 91 (PW91) exchange-correlation functional are presented. The structural and transport properties of liquid water are comparable to the previous results using Becke-Lee-Yang-Parr (BLYP) functional and experimental data. The shape and the position of the first peak in the oxygen–oxygen radial distribution function is in good agreement with the most recent neutron diffraction data. The ab initio molecular dynamics simulation of liquid water–vapor interface, which is the first of its kind, suggests a preferred orientation of the surface water dipole towards the bulk region.

This paper presents a detailed study of a water adlayer adsorbed on Pt(111) and Rh(111) surfaces using periodic density functional theory methods. The interaction between the metal surface and the water molecules is assessed from molecular dynamics simulation data and single point electronic structure calculations 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 conductivity—a result of a crucial importance for understanding the process of electron transfer through the water/metal interface and electrochemical 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 molecular 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 examined. 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 mixture 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 averages from molecular dynamics simulations.

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