Atomistic Modeling of Silver Clusters Formed on the Surface of AgBr

Abstract

A density functional calculation has been employed to describe silver clusters containing 1-5 atoms that are adsorbed to kink sites or flat regions that exist on the silver bromide (001) surface. The procedure self-consistently optimizes the positions of atoms in the silver cluster and the nearest several hundred crystal ions and improves over prior calculations by embedding quantum ions within a hemisphere of polarizable ions that are enclosed within a larger hemispherical array of several thousand point charges fixed at normal crystal sites. The calculated electron affinity values and adsorption energies for neutral silver clusters adsorbed near the positive kink site are increased but agree with earlier work that predicted photoelectron capture from the conduction band. It is shown that each step is exothermic for the mechanism of photoinduced silver cluster growth by alternate electron and then interstitial silver ion capture only at the positive kink. The electron and hole trap depths are reported and show a strong dependence upon the site of adsorption. Effects due to odd or even numbers of electrons in the silver cluster are observed at each surface site and give greater trap depths for electrons or holes at the odd-sized clusters. A number of reactions discussed in the literature were examined and shown to be consistent with these calculations.