Quantum Tunneling Rates of Gas-Phase Reactions from On-the-Fly Instanton Calculations.
The Journal of Physical Chemistry Letters
American Chemical Society
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Beyer, A., Richardson, J., Knowles, P., Rommel, J., & Althorpe, S. (2016). Quantum Tunneling Rates of Gas-Phase Reactions from On-the-Fly Instanton Calculations.. The Journal of Physical Chemistry Letters, 7 (21), 4374-4379. https://doi.org/10.1021/acs.jpclett.6b02115
The instanton method obtains approximate tunneling rates from the minimum-action path (known as the instanton) linking reactants to the products at a given temperature. An efficient way to find the instanton is to search for saddle-points on the ring-polymer potential surface, which is obtained by expressing the quantum Boltzmann operator as a discrete path-integral. Here we report a practical implementation of this ring-polymer form of instanton theory into the Molpro electronic-structure package, which allows the rates to be computed on-the-fly, without the need for a fitted analytic potential-energy surface. As a test case, we compute tunneling rates for the benchmark H + CH₄ reaction, showing how the efficiency of the instanton method allows the user systematically to converge the tunneling rate with respect to the level of electronic-structure theory.
A.N.B., J.O.R., and S.C.A. acknowledge funding from the UK Engineering and Physics Sciences Research Council. J.O.R. was supported by a European Union COFUND/Durham Junior Research Fellowship. J.B.R. thanks the Alexander von Humboldt Foundation for a Fedor-Lynen Fellowship.
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External DOI: https://doi.org/10.1021/acs.jpclett.6b02115
This record's URL: https://www.repository.cam.ac.uk/handle/1810/261883
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