Abstract: The theoretical steric energies E_s of the 64 hypothetical molecular sieves framework topological structures have been calculated by molecular mechanics method in this paper, these structures are several analogues of AlPO₄-5 family with orthorhombic system which had been designed recently. The results of calculated E_s are closely related to the framework structures themselves. The E_s of designed orthorhmbic AlPO₄-500 framework structure is the same as that of hexagonal AlPO₄-5 with the lowest E_s (-3447 kJ/mol).It means that the structure is the most stable one.The E_s of other two designed structures AlPO₄-562 and AlPO₄-557 E_s are lower(-3419 and -3418 kJ/mol respectively). It means that the two structures might be stable and, probably, they can be synthesized. We found that these E_s of designed structures are related with the order of interlaced up or down links of oxygen bridges on the interlayers of the structures. We suggested that the E_s can be used as a criterion of exist probability for designed hypothetical framework structures of molecular sieves.

Key words: AlPO₄-5, Topological structure, Steric energy