Diffusion of aromatic molecules in zeolite NaY .1. Constrained reaction coordinate dynamics

The diffusion of benzene and p-xylene in zeolite NaY at infinite dilution is studied by means of constrained reaction coordinate dynamics. Molecular dynamics (MD) simulations are used to determine the potential of mean force along the coordinate perpendicular to the window connecting two supercages of the zeolite. A comparison of the results of simulations with a fixed and with a flexible lattice shows that the consideration of lattice flexibility does not significantly influence the potential of mean force for cage-to-cage jumps. The changes in the orientation of the aromatic ring during the cage-to-cage jump are explicitly examined. The transition states for cage-to-cage migration are defined by a plane perpendicular to the reference coordinate. The components of the force along the reaction coordinate are studied as functions of the position, and the orientation is studied for the transition states. Differences between the results for benzene and p-xylene are discussed.