Correlation between electronic properties and reactivity toward oxygen of tetrahedral gold–silver clusters

The structure, electronic properties, and reactivity toward oxygen of Au19Ag and AuAg19 clusters are studied using relativistic DFT/PBE. Three isomers of Au19Ag and AuAg19 having a heteroatom on the top, an edge, and a facet are considered. Relative stability and reactivity of the mono-doped clusters are discussed in terms of the average atomic binding energy (Eb), the HOMO–LUMO gap, the adiabatic ionisation potential (IP), the electron affinity (EA), and the electrophilic Fukui functions are compared with those for bare Au20 and Ag20. The silver atom takes a position on the facet of the Au19Ag cluster, just as the gold atom takes an edge and the top sites of the AuAg19. The calculated values of Eb, HOMO–LUMO gap, IP, and EA decrease with increasing silver content in the cluster. The calculated adsorption energies of O2 on the clusters increase in the following order: Au20 < Au19Ag < Ag19Au ≈ Ag20. The chemical state of adsorbed oxygen depends on the cluster’s composition rather than on the heteroatom location. Dissociative oxygen adsorption is possible on Au19Ag, AuAg19, and Ag20.