Case Study Silica Sodalite

Synopsis of Nicholas et al. (1991) Molecular Modeling of Zeolite Structure. 2. Structure and Dynamics of Silica Sodalite and Silicate Force Field . 

Zeolites are mesoporous materials that are crystalline in nature. The simplest zeolites are made up of Al and/or Si and O atoms. Also known as molecular sieves, they find use as drying agents because they are very hygroscopic, but from an economic standpoint they are of greatest importance as size-selective catalysts in various reactions involving hydrocarbons and functionalized molecules of low molecular weight (for instance, they can be used to convert methanol to gasoline). The mechanisms by which zeolites operate 

0 fs time steps following 20 ps or more of equilibration at 300 K. Each MD trajectory is 20 ps, which is very short by modern standards, but possibly justified by the limited dynamics available within the crystalline environment. 

The authors finish by exploring the transferability of their force field parameters to a different zeolite, namely, silicalite. In this instance, a Fourier transform of the total dipole correlation function provides another model infrared (IR) spectrum for comparison to experiment, and again excellent agreement is obtained. Dominant computed bands appear at 1099, 806, 545, and 464 cm 1, while experimental bands are observed at 1100, 800, 550, and 420 cm 1. Some errors in band intensity are observed in the lower energy region of the spectrum. 

In conclusion, it appears that the majority of the most modem force fields do well in predicting structural and dynamical properties within wells on their respective PESs. However, their performance for non-equilibrium properties, such as timescales for conformational interconversion, protein folding, etc., have not yet been fully validated. With the increasing speed of both computational hardware and dynamics algorithms, it should be possible to address this question in the near future. 

---