Simulations of low-frequency vibrations of adsorbed molecules in zeolites

The role of the forcefield (FF) is critical in predicting the properties of supramolecular systems. Long time dynamic properties depend mostly on vibrations at low wavenumber: this is especially true for molecules adsorbed in zeolites, where low frequency vibrations partly control site-to-site jumps and hence kinetics. It is therefore essential that a FF devoted to study diffusion in zeolites reproduces this vibrational range, that can also be directly observed using inelastic neutron spectroscopy (INS). In this proceeding we present low frequency (LF) vibrational spectra of benzene adsorbed in NaY, as computed from molecular dynamics simulations, using three different FFs. We assess the variability of the spectra on the type of motion (librations and external vibrations,) temperature, local environment, and coupling to the zeolite phonons. A comparison to the experimental INS spectrum allows us to rank the FFs in their ability to reproduce benzene's kinetics in NaY.