Theoretical investigation on the structure and electronic properties of bimetallic gold-zinc cluster cations and their monocarbonyls

Abstract

Using the first principles calculations, the mixed AunZnm+ (n+ m = 6) cluster cations and their monocarbonyls AunZnmCO+ have been investigated at the PW91 level. For the small AunZnm+, most ground-state isomers are planar structures. A significant odd-even oscillation of the highest occupiedlowest unoccupied molecular orbital energy gaps with the number of Au atoms is observed. Upon CO adsorption, the top site and C head-on adsorptions are most favorable in energy. Moreover, the optimized geometries indicate that the CO molecule prefers binding to Au atom of the AunZnm+ clusters, which can be understood by the frontier molecular orbital theory in detail. From the theoretical calculations, the CO charge population, CO binding energy (BE) and the Gibbs free-energy change Delta G generally decrease with the increase of the Zn content. It is found that the BE is highly related to the electron transfer between CO and the cluster cations. Furthermore, a linear correlation between Delta G and the CO BE is found. The red shift in the CO stretching frequency is sensitive to the cluster size and composition. Our calculation suggests that CO reactive collision on Au3Zn+ and Au2Zn2+ may lead to the dissociation of the clusters with a Zn atom loss.