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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Path-dependent variational effects and multidimensional tunneling in multi-path variational transition state theory: rate constants calculated for the reactions of HO2 with tert-butanol by including all 46 paths for abstraction at C and all six paths for abstraction at O
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Path-dependent variational effects and multidimensional tunneling in multi-path variational transition state theory: rate constants calculated for the reactions of HO2 with tert-butanol by including all 46 paths for abstraction at C and all six paths for abstraction at O

机译：多路径变迁过渡状态理论中的路径相关变率效应和多维隧穿：通过包括C处所有46条提取路径和O处所有6条抽象路径计算HO2与叔丁醇反应的速率常数

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Multi-path variational transition state theory (MP-VTST) provides a conformationally complete framework for calculating gas-phase rate constants. For reactions in which the transition state has distinguishable torsional minima (which include most reactions), there are multiple possible reaction paths. In principle MP-VTST includes the contributions from all the reaction paths, and it should explicitly treat the variational and tunneling effects of each path, but in practice one may need to truncate the number of paths included in MP-VTST calculations in order to achieve a balance between computational cost and accuracy. In this work, we present calculations including all paths for two prototype combustion reactions, namely the two hydrogen abstraction reactions from tert-butanol by HO2 radical. For both reactions we included all the reaction paths. Since abstraction at C has 46 paths, it provided a good opportunity to carry out a case study in which we investigated the errors introduced by truncating the number of paths. For the reaction studied, we found that the variational and multidimensional tunneling transmission coefficients are very different for different reaction paths, which provides new evidence that MP-VTST is necessary for treating path-dependent variational effects and multidimensional tunneling. We found that tunneling transmission coefficients can be much larger for higher-energy paths than for lower-energy ones. Interestingly, the simple hypothesis that higher barriers are narrower does not explain this finding in the present case; we found instead that the effect is due to higher-energy barriers having the possibility of tunneling at energies farther below the barrier top. We also show that a previously applied criterion for judging convergence with respect to the number of paths may not be reliable at low temperature.
机译：多径变迁过渡态理论（MP-VTST）为计算气相速率常数提供了构象完整的框架。对于其中过渡态具有明显的扭转最小值（包括大多数反应）的反应，存在多种可能的反应路径。原则上，MP-VTST包括所有反应路径的贡献，它应明确处理每条路径的变化和隧穿效应，但实际上，可能需要截断MP-VTST计算中包括的路径数，以实现计算成本和准确性之间的平衡。在这项工作中，我们提出了包括两个原型燃烧反应的所有路径的计算，即两个由叔丁醇通过HO2自由基提取氢的反应。对于这两个反应，我们都包括了所有反应路径。由于C处的抽象具有46条路径，因此它为进行案例研究提供了一个很好的机会，在该案例中，我们研究了通过截断路径数而引入的错误。对于所研究的反应，我们发现不同反应路径的变分和多维隧穿传输系数非常不同，这提供了新的证据表明MP-VTST对于处理路径相关的变分效应和多维隧穿是必要的。我们发现，高能量路径的隧道传输系数可能比低能量路径的大。有趣的是，在当前情况下，较高的壁垒较窄的简单假设不能解释这一发现。相反，我们发现这种影响是由于高能垒具有在远低于势垒顶部的能量处隧穿的可能性。我们还表明，以前使用的判据关于路径数量的收敛性在低温下可能并不可靠。

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