Constrained Nuclear-Electronic Orbital Transition State Theory Using Energy Surfaces with Nuclear Quantum Effects

Area of Science:

• Chemical kinetics
• Quantum chemistry
• Theoretical chemistry

Background:

• Hydrogen-atom transfer is vital in chemistry and biology.
• Accurately modeling quantum effects like tunneling in these reactions is difficult.
• Existing methods struggle with precise kinetic isotope effect predictions.

Purpose of the Study:

• To develop a novel theoretical framework for predicting hydrogen-atom transfer reaction rates.
• To incorporate quantum mechanical effects, including zero-point energy and tunneling, into rate predictions.
• To validate the new method against experimental data for gas-phase reactions.

Main Methods:

• Combining transition state theory (TST) with constrained nuclear-electronic orbital (CNEO) theory to create CNEO-TST.
• Utilizing CNEO density functional theory (CNEO-DFT) for generating effective potential energy surfaces.
• Calculating reaction rate constants for gas-phase hydrogen-atom transfer and deuterated reactions.

Main Results:

• CNEO-TST accurately predicts reaction rates at room temperature.
• The method effectively includes zero-point energy and shallow tunneling effects.
• Computational scaling of CNEO-DFT makes the approach economical for large systems.
• Achieves accuracy comparable to advanced variational TST methods.

Conclusions:

• CNEO-TST is a valuable tool for predicting reaction rates, especially for reactions with significant quantum motion.
• The method is applicable to diverse chemical and biochemical processes involving hydrogen, proton, or hydride transfer.
• Offers a computationally efficient and accurate alternative for studying complex reaction dynamics.