A theoretical study of the twinned ZnO nanostructures

Abstract Zinc oxide (ZnO) based nanomaterials are widely used as heterogeneous catalysts. Particularly, the twinned ZnO nanomaterials have been shown to exhibit unique catalytic activities. In this work, we constructed the atomic models of three possible twinned ZnO nanostructures with different types of twinning boundaries and surface terminations (Zn-Zn-, O-O- and O-Zn-terminated). Theoretical simulations aided by evolutionary algorithm showed that the O-Zn-terminated “polar” nanostructure owns the highest stability, which is attributed to the saturated coordination numbers of the Zn and O atoms in the twinning boundary. Furthermore, structural and electronic calculations indicated that the total energies of the twinned ZnO nanostructures depend on both the surface and twinning boundary energetics, and the latter can play a more important role. From the calculated structures, we also found that the Zn-terminated surfaces of all the twinned structures can expose metallic-like Zn dimers which has the bond distance of ∼ 2.44 A only, which may act as the active sites for catalytic reactions.