Figure 1. (MgO)16 and (ZnO)16cluster models. (Color description Mg: yellow; O: red; Zn: cyan)
As shown in Fig. 1, the optimized structure of the (ZnO)16 cluster exhibits a feature similar to those of (MgO)16. Vibrational frequency calculation confirms that the structure of (ZnO)16 (Fig. 1) corresponds to the potential energy minimum. To check the possibility of other minima structures of (ZnO)16, we further applied one of the global optimization algorithms [32] implemented in the atomic simulation environment (ASE) program.[33,34] The result of the global optimization indicates that the structure shown in Fig. 1 is a global minima.