Graduation Year

2010

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Chemistry

Major Professor

Brian Space, Ph.D.

Co-Major Professor

Randy Larsen, Ph.D.

Committee Member

H. Lee Woodcock, Ph.D.

Committee Member

Preston Moore, Ph.D.

Keywords

MOF, hydrogen storage, atomic point charges, monopoles

Abstract

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.

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