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Anharmonic Correction to Free Energy Barriers from DFT-Based Molecular Dynamics Using Constrained Thermodynamic
Jonas Amsler1, Philipp N Plessow1, Felix Studt1,2
1Institute of Catalysis Research and Technology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Journal of Chemical Theory and Computation
|April 12, 2023
Summary
A new method, lambda-path integration (λ-TI), offers an efficient alternative for calculating free energy barriers in chemical reactions. This approach provides greater flexibility in choosing reference states, improving computational efficiency for catalysis research.
Area of Science:
- Computational Chemistry
- Theoretical Chemistry
- Physical Chemistry
Background:
- Calculating anharmonic contributions to free energy barriers is crucial for understanding reaction mechanisms.
- The established Blue Moon ensemble method (ξ-TI) integrates free energy gradients along a reaction coordinate.
- Limitations exist in ξ-TI regarding the choice of reference states for free energy barrier calculations.
Purpose of the Study:
- To introduce constrained thermodynamic λ-path integration (λ-TI) as an alternative to ξ-TI for calculating anharmonic free energy barriers.
- To benchmark λ-TI against ξ-TI for various chemical reactions.
- To highlight the advantages of λ-TI, particularly its flexibility in reference state selection for catalysis.
Main Methods:
- Development and application of the λ-path integration (λ-TI) method.
- Benchmarking λ-TI against the established ξ-TI method for several test reactions (ethane internal rotation, CH3Cl substitution, retro-Diels-Alder, zeolite proton transfer).
- Integration of the Bennett acceptance ratio method with λ-TI to assess computational efficiency.
Main Results:
- λ-TI showed good agreement with ξ-TI across all tested reactions.
- λ-TI allows for the use of virtually any reference state, unlike ξ-TI which is limited to initial coadsorbed states.
- Combining λ-TI with the Bennett acceptance ratio method reduces the number of integration grid points with tolerable accuracy, enhancing computational efficiency.
Conclusions:
- λ-TI is a viable and accurate alternative to ξ-TI for computing anharmonic free energy barriers.
- The flexibility in reference state selection makes λ-TI particularly advantageous for catalytic applications.
- λ-TI, especially when combined with the Bennett acceptance ratio method, offers improved computational efficiency over ξ-TI.
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