The Stability and Optical Gap of Zinc Oxide Clusters (ZnO)n (n=2-18)

The stability and the optical band gap of the Zinc Oxide clusters (ZnO)(n) (n = 2-18) are investigated by using density functional theory (DFT) and the time-dependent density functional theory (TD-DFT), respectively. The differences between the HOMO-LUMO gap (Delta(h-l)) and the optical gap (Delta(opt)) are dramatic for small clusters (2 <= n <= 5). As the increasing of the cluster size, the differences become small. The results indicate that the stability and the optical gap are related to the sizes and symmetries of the clusters. Further, it is shown that the structures have much greater impact on the optical gap, there is the dipole-forbidden transition in the optical gap for high symmetric structures.