Structural and Electronic Property Study of (ZnO)n, n ≤ 168: Transition from Zinc Oxide Molecular Clusters to Ultrasmall Nanoparticles

Abstract

Global minimum energy structures of (ZnO)n, n ≤ 168, were determined by using a hybrid genetic algorithm followed by a local geometry optimization at the density functional theory level. New “magic number” structures were found for the (ZnO)n clusters and ultrasmall nanoparticles. Particles with morphologies of single-, double-, and triple-layered octahedral cages exhibit higher stability than particles with other morphologies. (ZnO)132 and (ZnO)168 are found to be triple-layer cages with a diameter of ∼2 nm in each dimension. The normalized clustering energies (average cohesive energies) of the multilayered zinc oxide cages can be extrapolated to provide an estimate of the bulk limit. The surface energy densities of the ultrasmall nanoparticles are almost constant. The relatively high stability of the multilayered particles is attributed to the lack of terminal surface atoms and the effective interlayer stacking of hexagonal cells, as the layers in the particles are intact and hexagonally tiled. The epit...