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Published August 1, 1997 | Published
Journal Article Open

Prediction of bond dissociation energies and transition state barriers by a modified complete basis set model chemistry


The complete basis set model chemistries CBS-4 and CBS-q were modified using density functional theory for the geometry optimization step of these methods. The accuracy of predicted bond dissociation energies and transition state barrier heights was investigated based on geometry optimizations using the B3LYP functional with basis set sizes ranging from 3-21G(d,p) to 6-311G(d,p). Transition state barrier heights can be obtained at CBS-q with B3LYP/6-31G(d,p) geometries with rms error of 1.7 kcal/mol within a test set of ten transition state species. The method should be applicable to molecules with up to eight or more heavy atoms. Use of B3LYP/6-311G(d,p) for geometry optimizations leads to further improvement of CBS-q barrier heights with a rms error of 1.4 kcal/mol. For reference, the CBS-QCI/APNO model chemistry was evaluated and is shown to provide very reliable predictions of barrier heights (rms error=1.0 kcal/mol).

Additional Information

© 1997 American Institute of Physics. Received 2 December 1996; accepted 25 April 1997. This work was supported by the U.S. Environmental Protection Agency, Center on Airborne Organics, under agreement R-819714-01-0. T.P.W.J. gratefully acknowledges a Forschungsstipendium der Deutschen Forschungsgemeinschaft. We thank Mr. Kiran Shekar for performing GAUSSIAN94 calculations. Allocation of CPU time for the IBM SP/2 by the Center for Advanced Computing Research (CACR) at the California Institute of Technology is gratefully appreciated.

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