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Computational Spectroscopy and Molecular Dynamics Studies of Condensed-Phase Radicals Using Density Functional Theory

Rana, Bhaskar
http://rave.ohiolink.edu/etdc/view?acc_num=osu1639689998789038

Abstract Details

2021, Doctor of Philosophy, Ohio State University, Chemistry.
In the following work, we discuss the development and application of efficient techniques either aimed at extending the applicability of the currently available methods in the liquid phases to larger system sizes, or at eliminating the artifacts with the existing techniques for several open-shell systems encountered in condensed phases. First, we have investigated the local solvation structure of aqueous hydroxyl radical and absorption spectrum by employing both the mixed quantum mechanics\slash molecular mechanics (QM/MM) framework and periodic density functional theory (DFT) framework. Theoretically, the presence of a hemibond (a two-center, three-electron bond) in this system has been debated for a long time. This structural motif has been explained as either an artifact arising from the self-interaction error (SIE) in DFT or an artifact because of the finite-size effects of the simulation cell but shown to play an important role in the absorption spectrum based on some theoretical studies on smaller representative clusters. Our investigations based on simulations with various DFT simulations suggest that a pseudo-hemibonded motif still persists in this system. We have also demonstrated that the population of hemibonds is extremely sensitive to the amount of exact Hartree-Fock (HF) exchange employed in the simulation. However, we have concluded that these hemibonded motifs play an outsized role in the absorption spectrum, even when present as a rare configuration, due to an intense charge-transfer transition in the hemibonded structures. To eliminate the artifacts arising from this SIE, we have then implemented the density-corrected DFT (DC-DFT) formalism along its analytical gradient, which has been proven to be powerful for the systems with larger density-driven errors. Afterward, we have applied this technique for studying the electronic structure descriptions of the hole defects in Al-doped silica and electron-polarons in anatase titanium oxide where most of the standard DFT functionals fail. Using DC-DFT with some cluster models, we have been successful in describing the proper localized nature of the hole in Al-doped as well as the proper structural distortion around the defect centers. This method has also removed a lot of density-driven error in the case of anatase. Next, we have applied this technique to study the stability ordering of different polymorphs of several organic crystals where standard DFT functionals perform poorly, but the ordering gets improved with the density-corrected versions. Furthermore, we have also done some method development with the QM/MM-Ewald framework by using CM5 charges (charge-model 5) in an effort to push the existing framework in simulating systems with larger QM sizes and longer timescales.
John M. Herbert (Advisor)
Marcos Sotomayor (Committee Member)
Alexander Y. Sokolov (Committee Member)
201 p.
Chemistry; Physical Chemistry
Theoretical Chemistry; Electronic Structure Theory; Density Functional Theory; Molecular Dynamics; Computational Spectroscopy

Recommended Citations

Citations

  • Rana, B. (2021). Computational Spectroscopy and Molecular Dynamics Studies of Condensed-Phase Radicals Using Density Functional Theory [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1639689998789038

    APA Style (7th edition)

  • Rana, Bhaskar. Computational Spectroscopy and Molecular Dynamics Studies of Condensed-Phase Radicals Using Density Functional Theory. 2021. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1639689998789038.

    MLA Style (8th edition)

  • Rana, Bhaskar. "Computational Spectroscopy and Molecular Dynamics Studies of Condensed-Phase Radicals Using Density Functional Theory." Doctoral dissertation, Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1639689998789038

    Chicago Manual of Style (17th edition)

osu1639689998789038
76
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