Date of Award

12-2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemistry

Advisor

Stuart, Steven J

Committee Member

Dominy , Brian

Committee Member

McNeill , Jason

Committee Member

Latour , Robert

Abstract

ABSTRACT
A new hybrid bond-order potential for silicon is developed. The functional form of the potential is derived from hybrid of expressions from empirical bond-order formalism and first principles approximations. The total energy is expressed as the sum of attractive, repulsive and promotion energies. By introducing a screening function derived from approximations to first principles expressions, the potential is made long-ranged by allowing covalent interactions beyond the first nearest neighbor shell of atoms in agreement with quantum mechanical descriptions of the bonding in silicon. Environment-dependent promotion energy is introduced that accurately accounts for energetic interactions due to changes in hybridization state of atoms during chemical bonding. The treatment of the bond-order has been extended beyond the tight-binding second moment approximations to include screening of the bond strength between two atoms by other atoms in their vicinity.
A database consisting of structures, cohesive energies and promotion energies of clusters of 3-8 atoms, equations of state properties for 15 phases of silicon were used to obtain optimized parameters for the potential. The resulting model is able to accurately represent silicon in a wide range of bonding environments. The potential has been validated against widely used interatomic potentials for silicon in the literature for energies and structure of small clusters, equations of state for diamond cubic and other high pressure phases of silicon.

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