Theoretical prediction of low-frequency vibrations of extra-framework cations in mordenite zeolites

Abstract

Molecular dynamics simulations, using classical potential models to represent the cation-framework interactions, were performed in order to predict the low frequency region of vibrational spectra for mordenite zeolites. The position and the shape of the bands assigned to the cation vibrations have been studied as a function of the nature of the extra-framework charge balancing cations (alkali, alkaline earth) and of the Si/Al ratio characterizing the zeolite framework. The critical role of the forcefield is also demonstrated by computing the low frequency spectra using two different forcefields which include the flexibility of the host framework.