MOLECULAR-DYNAMICS SIMULATION STUDIES OF ZEOLITE-A - VI - VIBRATIONALMOTION OF NONRIGID ZEOLITE-A FRAMEWORK

In the present paper, we report a molecular dynamics (MD) simulation o f non-rigid zeolite-A framework only as the base case for a consistent study of the role of intraframework interaction on several zeolite-A systems using the same technique in our previous studies of rigid zeol ite-a frameworks. Usual bond stretching, bond angle bending, torsional rotational, and non-bonded Lennard-Jones and electrostatic interactio ns are considered as intraframework interaction potentials. The compar ison of experimental and calculated structural parameters confirms the validity of our MD simulation for zeolite-A framework. The radial dis tribution functions of non-rigid zeolite-A framework atoms characteriz e the vibrational motion of the framework atoms. Mean square displacem ents are all periodic with a short period of 0.08 ps and a slow change in the amplitude of the vibration with a long period of 0.53 ps. The displacement auto-correlation (DAC) and neighbor-correlation (DNC) fun ctions describe the up-and-down motion of the framework atoms from the center of alpha-cage and the back-and-forth motion on each ring windo w from the center of each window. The DAC and DNC functions of the fra mework atoms from the center of alpha-cage at the 8-ring windows have the same period of the up-and-down motion, but those functions from th e center of 8-ring window at the 8-ring windows are of different perio ds of the back-and-forth motion.