Density functional theory study of copper clusters

A density functional theory study of copper clusters is presented. Fully optimized geometries, electronic structures, HOMO-LUMO gaps, spin density distributions, and ionization potentials are reported. The study is systematic starting with one-dimensional clusters followed by several planar structures and three-dimensional systems chosen to emulate (100) and (111) planes of bulk Cu. For. the I-D systems, it is found that the dissociation energy and ionization potential follow an oscillatory behavior that reflects a conjugate-like character indicative of a pair-occupation nature of copper. Calculated bond lengths, vibrational modes, ionization potentials,and dissociation energies for the smallest clusters agree very well with the available experimental information. A 1-D limit is rapidly reached by a chain system of 15 atoms. Most of the analyzed properties show substantial differences between the end atoms and those occupying central locations. The chain central atoms, with largest coordination numbers, bear the highest negative charge in the linear chains, and the same feature is observed in planar and 3-D structures. A semiempirical expression dependent on the cluster average coordination number is used to investigate the connection between the calculated cluster ionization potential and the local work function. The study confirms the validity of the cluster approach to improve the understanding of physicochemical properties at interfaces.