Computer simulations of metal-organic frameworks are conducted to both
investigate the mechanism of hydrogen sorption and to elucidate a detailed,
molecular-level understanding of the physical interactions that can lead to successful
material design strategies. To this end, important intermolecular interactions are
identified and individually parameterized to yield a highly accurate representation
of the potential energy landscape. Polarization, one such interaction found to play a
significant role in H 2 sorption, is included explicitly for the first time in simulations
of metal-organic frameworks. Permanent electrostatics are usually accounted for by
means of an approximate fit to model compounds. The application of this method
to simulations involving metal-organic frameworks introduces several substantial
problems that are characterized in this work. To circumvent this, a method is
developed and tested in which atomic point partial charges are computed more
directly, fit to the fully periodic electrostatic potential. In this manner, long-range
electrostatics are explicitly accounted for via Ewald summation. Grand canonical
Monte Carlo simulations are conducted employing the force field parameterization
developed here. Several of the major findings of this work are: Polarization is found
to play a critical role in determining the overall structure of H 2 sorbed in
metal-organic frameworks, although not always the determining factor in uptake.
The parameterization of atomic point charges by means of a fit to the periodic
electrostatic potential is a robust, efficient method and consistently results in a
reliable description of Coulombic interactions without introducing ambiguity
associated with other procedures. After careful development of both hydrogen and
framework potential energy functions, quantitatively accurate results have been
obtained. Such predictive accuracy will aid greatly in the rational, iterative design
cycle between experimental and theoretical groups that are attempting to design
metal-organic frameworks for a variety of purposes, including H 2 sorption and CO2
sequestration.
| Identifer | oai:union.ndltd.org:USF/oai:scholarcommons.usf.edu:etd-4865 |
| Date | 14 July 2010 |
| Creators | Stern, Abraham C. |
| Publisher | Scholar Commons |
| Source Sets | University of South Flordia |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Graduate Theses and Dissertations |
| Rights | default |
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