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Georgia Tech

1. Temelso, Berhane. Computation of Molecular Properties at the Ab Initio Limit.

Degree: PhD, Chemistry and Biochemistry, 2007, Georgia Tech

The accuracy of a quantum chemical calculation inherently depends on the ability to account for the completeness of the one- and n-particle spaces. The size of the basis set used can be systematically increased until it reaches the complete one-particle basis set limit (CBS) while the n-particle space approaches its exact full configuration interaction (FCI) limit by following a hierarchy of electron correlation methods developed over the last seventy years. If extremely high accuracy is desired, properly correcting for very small effects such as those resulting the Born-Oppenheimer approximation and the neglect of relativistic effects becomes indispensable. For a series of chemically interesting and challenging systems, we identify the limits of conventional approaches and use state-of-the-art quantum chemical methods along with large basis sets to get the “right answer for the right reasons.” First, we quantify the importance of small effects that are ignored in conventional quantum chemical calculations and manage to achieve spectroscopic accuracy (agreement of 1 cm−1 or less with experimental harmonic vibrational frequencies) for BH, CH+ and NH. We then definitively resolve the global minimum structure for Li₆ , Li₆⁺ , and Li₆- using high accuracy calculations of the binding energies, ionization potentials, electron affinities and vertical excitation spectra for the competing isomers. The same rigorous approach is used to study a series of hydrogen transfer reactions and validate the necessary parameters for the hydrogen abstraction and donation steps in the mechanosynthesis of diamondoids. Finally, in an effort to overcome the steep computational scaling of most high-level methods, a new hybrid methodology which scales as O(N⁵) but performs comparably to O(N⁶) methods is benchmarked for its performance in the equilibrium and dissociation regimes. Advisors/Committee Members: Sherrill, C. David (Committee Chair), Brédas, Jean-Luc (Committee Member), Hernandez, Rigoberto (Committee Member), Merkle, Ralph C. (Committee Member), Whetten, Robert L. (Committee Member).

Subjects/Keywords: High accuracy; Hydrogen abstraction; Lithium hexamers; Computational chemistry; Quantum chemistry; Ab initio; Schrödinger equation; Quantum chemistry; Electronic structure; Chemistry, Physical and theoretical Data processing; Born-Oppenheimer approximation

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Temelso, B. (2007). Computation of Molecular Properties at the Ab Initio Limit. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/14638

Chicago Manual of Style (16th Edition):

Temelso, Berhane. “Computation of Molecular Properties at the Ab Initio Limit.” 2007. Doctoral Dissertation, Georgia Tech. Accessed April 02, 2020. http://hdl.handle.net/1853/14638.

MLA Handbook (7th Edition):

Temelso, Berhane. “Computation of Molecular Properties at the Ab Initio Limit.” 2007. Web. 02 Apr 2020.

Vancouver:

Temelso B. Computation of Molecular Properties at the Ab Initio Limit. [Internet] [Doctoral dissertation]. Georgia Tech; 2007. [cited 2020 Apr 02]. Available from: http://hdl.handle.net/1853/14638.

Council of Science Editors:

Temelso B. Computation of Molecular Properties at the Ab Initio Limit. [Doctoral Dissertation]. Georgia Tech; 2007. Available from: http://hdl.handle.net/1853/14638

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