First principles studies on the growth of small Cu clusters and the dissociative chemisorption of H2

The sequential growth of small copper clusters up to 15 atoms and the dissociative chemisorption of H2 on the minimum energy clusters are studied systematically using density functional theory under the generalized gradient approximation. We found that small Cun clusters grow by adopting a triangular growth pathway. The pentagon bipyramid structural arrangements are strongly favored energetically in the growth and the new addition in the cluster occurs preferably at a site where the atom is capable of interacting with more adjacent atoms. To understand the evolution of small copper clusters, we also performed calculations on selected icosahedral clusters (for n=13,19,25,55) and fcc-like clusters (n=14,23,32,41). By extrapolating/interpolating the binding energies of triangular clusters, icosahedral clusters, and bulk-like clusters, we found that structural transitions from the triangular growth clusters to the icosahedral and fcc-like clusters occur at approximately n=16 and n=32, respectively. Subsequently, we performed extensive calculations on the dissociative chemisorption of H2 on the minimum energy clusters. The chemisorption likely occurs near the most acute metal site with the two H atoms residing on the edges, which differs significantly from the chemisorption on Cu surfaces that usually takes place at the hollow sites.