Transition State Theory within Constrained Nuclear-Electronic Orbital Framework: Accurate Hydrogen Atom Transfer Reaction Rates with Direct Incorporation of Quantum Nuclear Delocalization Effects

Hydrogen atom transfer is crucial in a myriad of chemical and biological processes, yet 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 integrate traditional transition state theory (TST) with the recently 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 quantum delocalization effects, CNEO-DFT in combination with TST can accurately predict the hydrogen transfer reaction rates. Notably, this approach maintains computational efficiency comparable to conventional DFT-based TST but achieves accuracy comparable to more intricate DFT-based variational TST with tunneling corrections. Hence, CNEO-DFT combined with TST is a promising tool for future investigations of hydrogen atom transfer reactions within more complex chemical and biological systems.