Transition State Theory within Constrained Nuclear-Electronic Orbital Framework: Accurate Adiabatic Hydrogen Atom Transfer Reaction Rates with Incorporation of Zero-Point Energy Effects*

Hydrogen atom transfer is crucial in a myriad of chemical and biological processes. Nonetheless, the accurate and efficient descriptions of hydrogen atom transfer reactions remain highly challenging due to the significant nuclear quantum effects of hydrogen nuclei. In this paper, we combine traditional transition state theory (TST) with the newly developed constrained nuclear-electronic orbital density functional theory (CNEO-DFT) and predict the reaction rate constants for two prototypical gas phase hydrogen atom transfer reactions. We find that with a good description of nuclear quantum effects, especially the zero-point energy effect, CNEO-DFT in combination with TST can accurately predict the hydrogen transfer reaction rates with minimal computational cost. This high efficiency is in great contrast to conventional DFT-based TST, which requires the construction of a long reaction path and sophisticated correction schemes are needed to acchieve reasonable results. CNEO-DFT in combination with TST is a promising tool for future investigations of hydrogen atom transfer reactions in more complex chemical and biological systems.