Calculating rate constants with updated Hessians using variational transition state theory with multidimensional...

Area of Science:

• Chemical Kinetics
• Computational Chemistry
• Theoretical Chemistry

Background:

• Variational transition state theory with multidimensional tunneling (VTST/MT) is a key method for calculating reaction rate constants.
• Computational cost is a significant barrier in applying VTST/MT, limiting its widespread use.
• Existing methods for reducing computational cost often compromise accuracy.

Purpose of the Study:

• To develop and validate a computationally efficient strategy for calculating reaction rate constants using VTST/MT.
• To reduce the computational burden of geometry optimization and trajectory following procedures in VTST/MT.
• To assess the accuracy of the proposed method by comparing it with full Hessian calculations.

Main Methods:

• Utilizing updated Hessians to reduce computational costs in VTST/MT calculations.
• Addressing numerical instability issues with the Bofill update scheme near saddle points.
• Implementing a hybrid strategy: full Hessians in critical regions and updated Hessians along the minimum energy path (MEP).

Main Results:

• The proposed strategy significantly reduces computational costs for VTST/MT calculations.
• A mean unsigned percentage deviation (MUPD) of approximately 10% was observed for four studied reactions when full Hessians were computed up to 80% of the classical barrier height.
• The method allows for embarrassingly parallelization, enabling faster calculations on personal computer clusters.

Conclusions:

• The developed hybrid strategy effectively reduces computational costs in VTST/MT calculations while maintaining acceptable accuracy.
• This approach offers a practical and automatable solution for accelerating reaction rate constant calculations.
• The method enhances the accessibility and applicability of VTST/MT in chemical research.