Abstract: On the full optimization of geometry, the eight model clusters(including F^- held in the double four-membered ring and no F^-) have been peformed by using semi-empirical quantum-chemical PM3 method to obtain their geometric, electronic structures and stability. The influence of fluorine ion on structures and properties of four-membered ring has been examined. The stabilities of full Si, P-Al and P-Ga forming four-membered rings were found to be gradually increased with F^- encapsulation. However, the forming four membered ring for the Si-Al cluster is unstable. The calculated results show that the distances between F^- locating in the four-membered ring and framework elements are in agreement with the experimental values.

Key words: Zeolite molecular sieves, F^- ion, Double four membered ring, PM3 method, Structure and property