International Workshop on Dynamics in Confinement

J. Phys. IV France 10 (2000) Pr7-147-Pr7-150
DOI: 10.1051/jp4:2000729

Simulations of low-frequency vibrations of adsorbed molecules in zeolites

F. Jousse¹, S.M. Auerbach², H. Jobic³ and D.P. Vercauteren<sup>1

1</sup>  Laboratoire de Physico-Chimie Informatique, Facultés Universitaires de Namur, 61 rue de Bruxelles, 5000 Namur, Belgium
²  Department of Chemistry and Department of Chemical Engineering, University of Massachusetts, Amherst, MA 01003-4510, U.S.A.
³  Institut de Recherches sur la Catalyse, CNRS, 2 avenue Albert Einstein, 69626 Villeurbanne cedex, France

Abstract
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.

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