Properties of silver clusters adsorbed to silver bromide

Density functional calculations of the structure and electronic properties of silver clusters interacting with a fragment of silver bromide that is em bedded within a polarizable representation of the AgBr crystal are presente d. Flat (001) surfaces and kinked surfaces are considered. The optimized ge ometry of the silver clusters is nearly planar for the clusters up to four atoms that are considered. We examined the degree to which different surfac e defect sites could modulate the properties of the adsorbed silver cluster . The positive kink site is unique in providing a location where the neutra l cluster can capture photoelectrons. This effect can be rationalized by el ectrostatic arguments and is consistent with this site functioning as a loc ation for photolytic silver formation. Other kink sites of neutral or parti al negative charge do not permit electron trapping at neutral silver cluste rs. These sites could act as locations for chemically produced silver clust ers. Calculations are presented showing that some geometries of Ag-3(+) ads orbed at the negative kink can trap electrons in accord with a proposal by Tani. The calculations are used to compare different mechanisms for photoly tic formation of silver clusters. They can be compared to gas-phase calcula tions adjusted for the interaction with a polarizable surface to show that both calculations agree that cationic silver clusters are unstable with res pect to dissociation except on the negative kink. The calculations show a d eep electron trap depth for the silver atom consistent with its participati on in the nucleation phase of silver cluster growth during photolysis. A su lfide ion substituted for bromide at a positive kink is shown to provide a means of coupling the electron to the crystal ions.