A density functional study on cationic Au(n)Cu(m)+ clusters and their monocarbonyls.

Small cationic Au(n)Cu(m)+ (n + m < or = 6) clusters and their monocarbonyls Au(n)Cu(m)CO+ have been studied by first-principles calculations. The trend for small Au clusters to form planar structures is weaker when some Au atoms are substituted by Cu atoms. A significant odd-even oscillation of the electron affinity of the cationic clusters with the number of their Au or Cu atoms is observed. CO prefers binding to Cu, which can be understood by the frontier molecular orbital theory. Its binding energy on Au(n)Cu(m)+ generally decreases with the increase of the Cu content in the cluster, which is highly related to the electron transfer between CO and the cluster. Our calculation suggests that reactive collision between CO and Au3Cu+ may lead to the dissociation of the cluster with an Au atom loss.