MOLECULAR-DYNAMICS SIMULATION OF ZEOLITE NAY - A STUDY OF STRUCTURE, DYNAMICS, AND THERMALIZATION OF SORBATES

A force field is presented for zeolite NaY, accounting for the flexibility of the lattice. It is mainly based on effective pair potentials between neighboring atoms. The comparison of calculated and experimental data shows that the main structural and dynamical properties of the zeolite are reproduced. Due to its computational economy the model can be used for molecular dynamics (MD) simulations of zeolite/sorbate systems, thus overcoming the problems arising from the assumption of fixed frameworks. Here the flexibility of the inner void space is studied at several temperatures by considering the diameter and the area of the windows connecting adjacent supercages. Furthermore we demonstrate with two examples, xenon and methane, the thermalization properties of the flexible framework. For comparison the mutual interaction of the sorbates at a loading of 1 particle/supercage is studied. For these investigations nonequilibrium MD simulations are performed. It is shown that the thermalization of the guests, due to their interaction with the modes of the framework, is stronger than their mutual interaction.