Small clusters of II-VI materials: Zn_iO_i, i=1–9

Improvements in the characterization of II-VI compound-based solar cells, and the recent experimental characterization of small clusters and nanoparticles, make the study of small II-VI clusters very interesting. In this work, the ground states of small Zn_iO_i clusters are studied, where i=1–9. Ringlike structures have been found to be the global minima for clusters as large as i=7, and three-dimensional spheroid structures for larger ones, where i=8 and 9. This is due to the stability of obtuse O-Zn-O angles in the first case, and to the stability gained from higher coordination in the second case. Three-dimensional structures may be envisioned as being built from Zn₂O₂ and Zn₃O₃ rings, as was the case for ZnS three-dimensional global minima and other ZnO calculations. Calculated natural orbital charges become larger as the cluster size increases, showing a tendency toward bulk charges.