Term of Award
Master of Science, Applied Physical Science
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Thesis (restricted to Georgia Southern)
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This work is licensed under a Creative Commons Attribution 4.0 License.
Department of Chemistry
Ryan C. Fortenberrey
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Explicitly correlated coupled cluster singles, doubles, and perturbative triples level [CCSD(T)-F12] and second-order closed-shell Møllar-Plesset perturbative theory (MP2-F12) anharmonic vibrational frequencies are compared with gas phase experiment and higher-level computations. These involve CCSD(T) with the complete basis set limit extrapolation along with, an additive factor for the energy difference between core and noncore electrons and a similar additive difference for scalar relativity to give the CcCR approach. One hundred and sixty-nine vibrational frequencies are computed using CCSD(T)-F12 with the aug-cc-pVTZ basis set. For MP2-F12 twenty-five molecules are examined under aug-cc-pVDZ basis set. The CCSD(T) computational analysis of the closed-shell molecules’ anharmonic vibrational frequencies resulted in a mean absolute error of 7.5 cm-1 between the CCSD(T)-F12 and CcCR. Comparison of the CCSD(T)-F12 with gas phase experiment gave mean absolute error of 5.8 cm-1 for twenty-nine closed-shell vibrational frequencies. However, the total computational time is reduced by more than 4 orders of magnitude when utilizing CCSD(T)-F12 as opposed to CcCR. From the computation, it is clear CCSD(T)-F12 correlated wave function is superior to MP2-F12, that this approach is a viable means of computing anharmonic vibrational frequencies of molecules when CcCR is not feasible to use.
Agbaglo, Donatus A., "The Performance of Explicitly Correlated Wavefunction for the Computation of Anharmonic Vibrational Frequencies" (2019). Electronic Theses and Dissertations. 1940.
Research Data and Supplementary Material