Bao, Junwei2018-11-282018-11-282018-09https://hdl.handle.net/11299/201082University of Minnesota Ph.D. dissertation.September 2018. Major: Chemistry. Advisor: Donald Truhlar. 1 computer file (PDF); xxvii, 788 pages.Chemical kinetics is of fundamental importance in chemical science. In this thesis, I will cover our recent theoretical developments in thermochemical kinetics, including kinetics theories at the high-pressure-limit, pressure-dependent reaction rate theories, and the tests and developments of new electronic-structure theories. For the high-pressure-limit theories, I will cover our works on multi-path variational transition state theory (VTST), its extension to treat chiral molecules, path-dependent variational effects and quantum mechanical tunneling, and our further development of dual-level multistructural coupled torsional potential anharmonicity (MS-T) theory. For the pressure-dependent rate theories, I will introduce the system-specific quantum RRK (SS-QRRK) theory, with chemical activation and thermal activation theories. In the area of electronic structure theories, I will cover our recent works on multiconfiguration pair-density functional theory (MC-PDFT). In this thesis, I also include a number of applications in which we applied the above-mentioned theories to chemically important systems. The applications in chemical kinetics include combustion chemistry, atmospheric chemistry and nanodusty plasma chemistry; and the applications of electronic-structure theories include transition metal chemistry, catalysis, and spin splitting of atmospherically important divalent radicals.enMulticonfiguration pair-density functional theoryMultidimensional tunnelingSystem-specific quantum RRK theoryTorsional anharmonicityVariational transition state theoryThesis or Dissertation