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Spin-flip time-dependent density functional theory and its applications to photodynamics

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2016, Doctor of Philosophy, Ohio State University, Chemistry.
In order to correctly simulate photodynamics, it is required to use first-principle methods since multiple electronic states have to be considered at the same time. As such, instead of computationally inexpensive classical molecular dynamics simulations, usually expensive ab initio molecular dynamics (AIMD) simulations become the only choice. For an excited-state AIMD simulation with the system including more than twenty heavy atoms, the only affordable quantum chemical method that is able to generate reasonable results may be the linear-response time-dependent density functional theory (LR-TDDFT). Other methods are either computationally too expensive (e.g. multireference methods) or unable to correctly describe the potential surfaces for both ground and excited electronic states (e.g. configuration interaction singles). However, conventional LR-TDDFT is not capable of describing the correct topology of conical intersections, where nonadiabatic transitions between electronic states take place. The simplest remedy is to use the “spin-flip” (SF) generalization of TDDFT, originally developed to investigate diradicals with strong static correlation in their ground states. This method treats the ground and excited states on an equal footing which thereby guarantees the correct topology at conical intersections. Recent computational studies have shown good performance of SF-TDDFT in describing electronic excitation energies, conical intersections, and excited-state reaction pathways. It may also be attractive to directly simulate photochemical or photophysical events through nonadiabatic AIMD simulations. Usually, these simulations require the calculation of nonadiabatic derivative couplings (NDCs), which are available only for a few electronic structure theory methods. Here, we present the formal derivations and implementations of the NDCs for both LR-TDDFT and SF-TDDFT. We also applied SF-TDDFT to study the ultrafast nonradiative decay of uracil solvated in aqueous solution, and proposed the deactivation mechanism to explain the experimentally observed different excited-state lifetimes of gas-phase and solvated uracil. Finally, the spin-adapted version of SF-TDDFT has been developed, which cures the spin contamination problem of the conventional SF-TDDFT. Preliminary calculations show that this new method is potentially promising for nonadiabatic AIMD simulations.
John Herbert (Advisor)
Sherwin Singer (Committee Member)
Marcos Sotomayor (Committee Member)
182 p.

Recommended Citations

Citations

  • Zhang, X. (2016). Spin-flip time-dependent density functional theory and its applications to photodynamics [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469628877

    APA Style (7th edition)

  • Zhang, Xing. Spin-flip time-dependent density functional theory and its applications to photodynamics. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1469628877.

    MLA Style (8th edition)

  • Zhang, Xing. "Spin-flip time-dependent density functional theory and its applications to photodynamics." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469628877

    Chicago Manual of Style (17th edition)