THEORETICAL STUDY ON THE MODIFICATION OF ACTIVE SITES IN GOLD SURFACES MODELED AS FINITE CLUSTERS. INFLUENCE OF STRUCTURAL DEFECTS AND THE APPLIED OVERPOTENTIAL

摘要

We report a description of the reactivity of a gold surface from theoretical calculations. This surface has been modeled with finite clusters, keeping the fcc crystal structure. The clusters are built with one, two or four unit cells. The influence exerted by structural defects and excess charge (to model an applied overpotential), on the density distribution in the surface, is analyzed. To describe the surface reactivity we employ reactivity indices from Density Functional Theory such as the Fukui functions and the condensed local softnesses. These were computed at an abinitio Hartree-Fock level, using the pseudopotentials of Hay and Wadt. From our numerical results we can conclude that the active sites may be clearly defined and pin-pointed. The cluster charge substantially modifies the distribution and position of the active sites, leading to changes in the active sites distribution from on top to on hollow or on bridge positions, depending on the cluster charge. Furthermore, it is observed that the presence of structural defects greatly modify the HOMO density close to the defect and this can be used to explain to some extent the superficial diffusion phenomenon experimentally observed, as well as the adsorption of ions in some specific surface sites.