Rings, towers, cages of ZnO

Theoretical electronic structure studies on (ZnO)(n) (n= 2-18, 21) have been carried out to show that the transition from an elementary ZnO molecule to the bulk wurtzite ZnO proceeds via hollow rings, towers, and cages. Our first principles electronic structure calculations carried out within a gradient corrected density functional framework show that small ZnnOn (n=2-7) clusters form single, highly stable rings. Zn3O3 and the symmetric cage Zn12O12 are shown to be particularly stable clusters. Among larger clusters, the most stable are oblong cages, Zn15O15, Zn18O18, and Zn21O21, which are reminiscent of nanotubes.