Evolution of Small Copper Clusters and Dissociative Chemisorption of Hydrogen

The structural evolution of small copper clusters of up to 15 atoms and the dissociative chemisorption of ${\mathrm{H}}_2$ on the minimum energy clusters are studied systematically using density functional theory. The preferred copper sites for chemisorption are identified and the transition state structures and activation barriers for clusters four to nine atoms are determined and found to be inconsistent with the empirical Brønsted-Evans-Polanyi relationship. The physicochemical properties of the clusters are computed and compared with the bulk and surface values. The results indicate that a phase transition must occur in the going from cluster to bulk.

Figure 1

The calculated lowest energy structure of Cu clusters.

Figure 2

(a) The calculated binding energy of ${\mathrm{C}\mathrm{u}}_n$ clusters per Cu atom. (b) Ionization potential (IP). (c) Electron affinity (EA). Both IP and EA exhibit even-odd alternation.

Figure 3

Calculated density of states. The solid line represents the occupied bands, and the dotted line is for the unoccupied bands.

Figure 4

The calculated lowest energy chemisorption structure of ${\mathrm{H}}_2$ on the lowest energy structure of ${\mathrm{C}\mathrm{u}}_n$ clusters.

Figure 5

The calculated dissociative chemisorption energy of ${\mathrm{C}\mathrm{u}}_n$.