Structural and optoelectronic properties of unsaturated ZnO and ZnS nanoclusters

Abstract

We report a systematic computational study of the structural and optoelectronic properties of unsaturated ZnO and ZnS nanoclusters with hexagonal prism structure, as a function of length and diameter. We computed the fundamental gap using density functional theory (DFT) in the framework of the ?SCF scheme and the optical gap by means of time-dependent DFT (TDDFT). We found that all ZnO nanostructures transform from wurtzite to graphitic phase. On the contrary, ZnS nanocrystals with diameters above ∼1 nm are found to transform to a zeolite BCT phase. These different structural properties reflect in a very different size dependence of the electronic and optical properties, with a strong discontinuity for ZnS particles. The correlation between morphology and optoelectronic properties is demonstrated by considering models of saturated clusters preserving the wurtzite phase. We additionally compared DFT/TDDFT results with many-body perturbation theory methods showing a general good agreement among the two techniques for this class of nanocrystals of the two materials. © 2012 American Chemical Society.