Pushing the ab initio limits for the accurate characterization of small molecular systems

by Yudong Qiu

Institution: University of Georgia
Year: 2015
Keywords: Computational chemistry
Posted: 02/05/2017
Record ID: 2106185
Full text PDF: http://purl.galileo.usg.edu/uga_etd/qiu_yudong_201505_phd


Modern quantum chemistry has merged as one of the most important tools for understanding and predicting various properties of chemical systems. Highly accurate ab initio methods like CCSD(T) provide quantitative theoretical predictions that can be used to assist or even guide the experiments. Herein, state-of-the-art ab initio methods are applied on two small molecular systems. In the characterization of the simplest metal carbene, BeCH2, energetic properties are investigated employing coupled cluster methods up to CCSDTQ and extrapolated to complete basis set limit using focal point analysis (FPA). Additionally, states with strong multi-reference characters are studied using MRCISD method with large basis sets. In another study, the reactions involved in the formation of BH26+ are investigated exhaustively. H2 binding energies determined using FPA agree perfectly with experiments. Furthermore, the previous discrepancy on activation energies is essentially solved by computing the insertion reaction rates with tunneling effects. Advisors/Committee Members: Henry F. Schaefer, III.