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Improved Density Functional Tight Binding Potentials for Metalloid Aluminum Clusters

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Naval Postgraduate School Monterey United States

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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 metalmetal bonds as well as organometallic components. We show that current DFTB parametrizations of the repulsive potential for AlC 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 Alcyclopentadienyl bond. DFTB molecular dynamics simulations of the oxidation of Al4Cp4 show reasonable comparison with a DFT-based Car-Parrinello method, including correct prediction of hydride transfers from Cp to the metal centers during the reaction.

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Technical Report



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Approved For Public Release;

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