Comparison of Siliceous Zeolite Potentials from the Perspective of Infrared Spectroscopy

Zeolites - microporous crystalline aluminosilicate materials - are the basis of many physical and chemical processes. Computational modeling of these processes requires an accurate description of the zeolite structure and the potential energy surface. In this work, two published force fields, the modified Zimmerman, Head-Gordon, and Bell (MZHB) potential [Sahoo and Nair, J. Comput. Chem. 2015, 36, 1562-1567] and the core-shell model [Schröder and Sauer, J. Phys. Chem. 1996, 100, 11043-11049], are tested in terms of their abilities to predict the structural and dynamical properties, including infrared (IR) spectra, of five silica polymorphs (three siliceous zeolites: zeolite Y, sodalite, and silicalite-1, as well as α-quartz and α-cristobalite) via classical molecular dynamics simulations. Normal mode analysis at the Γ point and quantum mechanical cluster calculations are carried out on periodic crystals and a finite-size representative cluster model, respectively, to assist in the assignment of IR bands. We observe that the core-shell model predicts a broader distribution of bond angles because of the lack of three-body interactions defined for the Si-O-Si angles. The MZHB potential, in contrast, consistently shifts angle-bending modes to higher wavenumbers relative to experiments.