Comparative density functional theory studies of Cu clusters

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.