Simulation of Physical Properties of Zeolitic Lattices

摘要

The use of atomistic potentials to calculate physical properties of the frameworkof zeolite materials with a SiO2 or AlPO4 composition is described. Emphasis is put on vibrational properties of the zeolite framework and the details of lattice energy minimized structures as a test for the potentials. The combination of experimental data and calculations of various properties using these potentials is shown to be valuable for the structure determination of zeolites. In chapter 2 and 3 two potentials for silica (the rigid ion potential and the shell model potential) are evaluated by means of the vibrational spectra of alpha-quartz and two pure silica zeolites. The analysis of vibrational spectra of zeolitic systems is also explored in chapter 4 using a Generalized Valence Force Field (GVFF), but on the level of large scale structural characteristics. The applicability of the rigid ion model, the shell model, the GVFF and a new potential (the partial charge model) on unusual structures, zeolitic silica polymorphs containing three membered rings, is illustrated in chapter 5. Chapter 6 describes the use of a combination of calculations and experimental data on elastic constants and thermal ellipsoids (anisotropic temperature factors) to refine the structure of the clathrasil Dodecasil-3C. Clathrasils are pure silica systems which are closely related to zeolites. The methods applied to model pure silica systems can also be used for AlPO4 structures. This is illustrated in chapter 7 and 8.