The structural and electronic properties of small Cu clusters were studied using density functional theory (DFT) calculations. The Cu clusters consist of up to fifty-five atoms with linear, planar, and three-dimensional structures. Five functionals, the Perdew-Wang 91 form of the generalized gradient approximation (PW91), Perdew-Burk-Ernzerhof functional (PBE), and three Minnesota functionals (M05, M06, and M06-L) were used. The dispersion correction in the format of DFT-D3 was also taken into account to the results of the PBE. The binding energy, average bond length, magnetic moment, and the HOMO-LUMO gap of each cluster were obtained and compared. DFT results for PBE and PW91 are very similar and agree with experimental data well. DFT-D3 corrections have no effect on the stable sequence. The copper clusters are more stable in the planar structure for clusters with n≤6, which agrees with other theoretical studies. In the case of bigger clusters, different DFT methods predicted different most stable structures. As cluster size increases, there was a monotonic decrease in magnetic moment for the odd number of clusters. As the linear cluster size increases, the bond distances between the atoms begin to alternate.

To understand the interaction between the Cu clusters and the ZnO substrate, we performed density functional theory (DFT) calculations on the adsorptions of small copper clusters on the ZnO(100) surface. The PBE functional was used in the DFT calculations with a plane wave basis set. The structural changes of the Cu clusters upon adsorption on the ZnO surface were provided. Although a few different adsorption sites are available, a single Cu atom was found to be adsorbed on three positions on a ZnO(100) surface. The adsorption strength of a Cu dimer is increased with respect to the adsorption of a single Cu atom. In the adsorptions of tetramers, and pentamers, three-dimensional configurations of Cu clusters are more favorable than the planer.