In this thesis, we study the feasibility of improving aluminum-carbon repulsive potentials for use in density-functional tight binding (DFTB) simulations of low-valence aluminum metalloid clusters. These systems are under consideration for use as novel fuels with rapid metal combustion kinetics, and contain an unusual mix of low-valence metal/metal bonds as well as organometallic components. We show that current DFTB parametrizations of the repulsive potential for Al/C interactions do not provide an adequate treatment of the bonding in these clusters. We performed a re-parametrization of the Al-C repulsive potential via comparison to high-level density functional theory (DFT) results that are known to give accurate thermochemistry for these clusters. We found that the reparametrized system solves the most egregious issues, particularly those associated with an unphysical distortion of the _5 Al/cyclopentadienyl bond. DFTB molecular dynamics simulations of the oxidation of Al4Cp*4 show reasonable comparisonwith a DFT-based Car-Parrinello method, including correct prediction of hydride transfers from Cp* to the metal centers during the reaction.
Naval Postgraduate School
Master of Science in Applied Physics
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