Interaction of halogens with Hg, Ag and Pt surfaces: a density functional study

The interaction of F. Cl, Br and I with three common electrode surfaces (mercury. silver, and platinum) is studied by ab initio density functional methods. The adsorption strength increases in the order I<Br<Cl<F, with silver as the metal having the highest affinity for the halogens, and platinum the low est. We ascribe the low affinity of halogens for platinum to the high work function of platinum. Tho importance of considering halogen binding energies instead of halide binding energies is illustrated, and it is shown how the study of the interaction of halides with small metal clusters may lead to results having only limited relevance to uncharged extended metal surfaces. Because of the importance of the electrostatic interaction, the absence of water in our (and previous) calculations makes it difficult to apply these results directly to the metal-solution interface. A simple tight-binding scheme that accounts for the different interactions with metal sp- and d-bands is suggested to reproduce some of the main trends of the ab inito calculations. This model may be of future applicability in the modeling of electrochemical interfaces. (C) 1999 Elsevier Science B.V. All rights reserved.