Molecular dynamics studies on zeolites. 3. Dehydrated zeolite A

Abstract

A model potential in two forms (harmonic and anharmonic) is proposed to be used in molecular dynamics simulations of silicate frameworks. This model is applied to the calculation of structural and vibrational properties of the anhydrous phase of Linde 2Mite 4 A. Our system is formed by a cubic box corresponding to one crystallographic cell containing 662 atoms without constraints. The results are compared with experimental data. The proposed models satisfactorily reproduce the main features of the aluminosilicate framework structure and dynamics.

Molecular simulation of loading-dependent diffusion in nanoporous materials using extended dynamically corrected transition state theory

“…In Fig. 18 we show the self-diffusivity of ethane using the Lennard-Jones ͑LJ͒ parameters of Table II and compare the results of a rigid zeolite to the flexible model of Demontis et al 60,61 Error bars are smaller or comparable to the symbol size. We have added the results of Schüring et al 43 for the infinite dilution case, and for 1 molecule"cage.…”

Simulating the Adsorption Isotherms of Methane, Ethane, and Propane in the Zeolite Silicalite

“…These Henry coefficients are in good agreement with the ones which have been calculated directly. 25 give a good prediction of the heat of adsorption, the adsorption isotherm differs significantly from the experimental data. Apparently a good prediction of the heat of adsorption does not guarantee an accurate description of the adsorption isotherm as well; for the development of a model it is important to compare the Henry coefficients with experimental data as well.…”

“…16, 25 We expect that this framework flexibility can be of importance for the modeling of the diffusion of the molecules, since a flexible framework may reduce the diffusion barriers. Since these barriers correspond to positions in which the molecules have a relatively high energy and therefore do not contribute much to the equilibrium properties, it can be expected that the assumption of a rigid zeolite lattice is less severe for these properties.…”

Electric-field-dependent empirical potentials for molecules and crystals: A first application to flexible water molecule adsorbed in zeolites

“…We attempted our first MD simulation of water in zeolites 13 in 1986 by selecting natrolite, a natural fibrous zeolite 10 whose structure 14 and properties 10 are known, and by testing some available point charge models for flexible water. The structure of natrolite is represented in Fig.…”

“…Contrary to this trend, the HOH angle diminished, and the internal stretching vibration frequencies became higher. 13 Apparently, the inclusion of a nonlinear polarization effect modifying the electronic distribution of the molecule and affecting its structure and bond strength was necessary in order to explain the observed phenomena.…”