Derivation of an interatomic potential for germanium- and silicon-containing zeolites and its application to the study of the structures of octadecasil, ASU-7, and ASU-9 materials

An interatomic potential for Ge/Si-zeolites has been developed by fitting to the experimental properties of quartz, GeO2(quartz), and GeO2(rutile). Testing the force field by comparison of the experimental and computed structural properties of octadecasil, ASU-7, and ASU-9 shows errors within 1-2% in the cell parameters and interatomic distances. Furthermore, Ge-O-Ge angles are well reproduced and predicted to lie within the range of 130-138degrees as compared to the experimental values in the range 126-140degrees. The force field can be used for new zeotype structures containing germanium and silicon as tetrahedral atoms in order to predict structural properties, as well as the energetic stability of different Ge and Si orderings. Improved accuracy is achieved, relative to earlier force fields, through the use of different polarizabilities for the oxide ion in distinct environments.