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Following our previous study of prototypical insertion reactions of energetically asymmetric type with the RPMD (Ring-Polymer Molecular Dynamics) method [Y. Li, Y. Suleimanov, and H. Guo, J. Phys. Chem. Lett. 5, 700 (2014)], we extend it to two other prototypical insertion reactions with much less exothermicity (near thermoneutral), namely, (X + H2) → HX + H(X = C(¹D), S(¹D), in order to assess the accuracy of this method for calculating thermal rate coefficients for this class of reactions. For both chemical reactions, RPMD displays remarkable accuracy and agreement with the previous quantum dynamic results that make it encouraging for the future application of the RPMD to other barrier-less, complex-forming reactions involving polyatomic reactants with any exothermicity. [ABSTRACT FROM AUTHOR]

This Feature Article presents an overview of the current status of ring polymer molecular dynamics (RPMD) rate theory. We first analyze the RPMD approach and its connection to quantum transition-state theory. We then focus on its practical applications to prototypical chemical reactions in the gas phase, which demonstrate how accurate and reliable RPMD is for calculating thermal chemical reaction rate coefficients in multifarious cases. This review serves as an important checkpoint in RPMD rate theory development, which shows that RPMD is shifting from being just one of recent novel ideas to a well-established and validated alternative to conventional techniques for calculating thermal chemical rate coefficients. We also hope it will motivate further applications of RPMD to various chemical reactions. [ABSTRACT FROM AUTHOR]

Thermal rate coefficients and kineticisotope effect have been calculated for prototypical heavy–light–heavypolyatomic bimolecular reactions Cl + CH4/CD4→ HCl/DCl + CH3/CD3, using a recentlyproposed quantum dynamics approach: ring polymer molecular dynamics(RPMD). Agreement with experimental rate coefficients, which are quitescattered, is satisfactory. However, differences up to 50% have beenfound between the RPMD results and those obtained from the harmonicvariational transition-state theory on one of the two full-dimensionalpotential energy surfaces used in the calculations. Possible reasonsfor such discrepancy are discussed. The present work is an importantstep in a series of benchmark studies aimed at assessing accuracyfor RPMD for chemical reaction rates, which demonstrates that thisnovel method is a quite reliable alternative to previously developedtechniques based on transition-state theory. [ABSTRACT FROM AUTHOR]

Review: 109 refs. [ABSTRACT FROM AUTHOR]

The rate constant for the H atom abstraction reaction from methane by the muonic helium atom, Heμ + CH4 → HeμH + CH3, is reported at 500 K and compared with theory, providing an important test of both the potential energy surface (PES) and reaction rate theory for the prototypical polyatomic CH5 reaction system. The theory used to characterize this reaction includes both variational transition-state (CVT/μOMT) theory (VTST) and ring polymer molecular dynamics (RPMD) calculations on a recently developed PES, which are compared as well with earlier calculations on different PESs for the H, D, and Mu + CH4 reactions, the latter, in particular, providing for a variation in atomic mass by a factor of 36. Though rigorous quantum calculations have been carried out for the H + CH4 reaction, these have not yet been extended to the isotopologues of this reaction (in contrast to H3), so it is important to provide tests of less rigorous theories in comparison with kinetic isotope effects measured by experiment. In this regard, the agreement between the VTST and RPMD calculations and experiment for the rate constant of the Heμ + CH4 reaction at 500 K is excellent, within 10% in both cases, which overlaps with experimental error. [ABSTRACT FROM AUTHOR]