ANALYSIS OF STRUCTURAL VIBRATIONS OF AN NAX ZEOLITE - FORCE-FIELDS

An analysis of the framework vibrations of NaX zeolite has been carried out by means of a normal coordinate treatment for selected tetrahedral, ditetrahedral and 6-ring cluster models. Besides the bond length scaled force field (BLSF) usually used we have taken into account the adjusted valence force field (AVFF) and the effective nuclear charge model (ENCM), allowing to introduce additionally interaction force constants in a systematic way. The AVFF and the BLSF are especially suited for reproduction of the vibrational frequencies obtained experimentally. The nature of the normal vibrations, obtained from the potential energy distribution and the eigenvectors, is characterized in a similar manner within all the force field models investigated.