Path integral evaluation of the quantum instanton rate constant for proton transfer in a polar solvent.
Path integral evaluation of the quantum instanton rate constant for proton transfer in a polar solvent.
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DOI：
10.1063/1.1832598
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发表时间：
2005-01
期刊：
影响因子：
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通讯作者：
Takeshi Yamamoto;W. Miller
中科院分区：
文献类型：
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作者：
Takeshi Yamamoto;W. Miller
热速率常数的量子瞬子近似是量子跃迁态理论（QTST）的一种，应用于Azzouz和Borgis建立的液态氯甲烷中质子转移反应模型。使用蒙特卡罗路径积分方法进行计算，并使用本路径积分方法对其他两个密切相关的QTST，即质心密度和Hansen-Andersen QTST进行评估以进行比较。然后介绍了一种直接通过速率相对于氢质量的热力学积分来计算动力学同位素效应的技术，这种技术具有避免昂贵的活化自由能评估的实际优点。目前对Azzouz-Borgis问题的应用表明，上述三种类型的QTST在速率上提供了非常相似的结果，彼此在30%以内，考虑到这些QTST的完全不同的推导，这是非常重要的；后一种速率也与先前的一些其他结果（例如，通过具有量子跃迁的分子动力学获得的结果）在大约2(7)的H(D)转移因子内合理地一致，从而显着减小了精确速率的可能范围。此外，发现以往研究中Azzouz-Borgis模型的参数化存在很小但不可忽略的不一致性，导致计算率存在较大的明显差异。
The quantum instanton approximation for thermal rate constants, a type of quantum transition state theory (QTST), is applied to a model proton transfer reaction in liquid methyl chloride developed by Azzouz and Borgis. Monte Carlo path integral methods are used to carry out the calculations, and two other closely related QTST's, namely, the centroid-density and Hansen-Andersen QTST, are also evaluated for comparison using the present path integral approach. A technique is then introduced that calculates the kinetic isotope effect directly via thermodynamic integration of the rate with respect to hydrogen mass, which has the practical advantage of avoiding costly evaluation of the activation free energy. The present application to the Azzouz-Borgis problem shows that the above three types of QTST provide very similar results for the rate, within 30% of each other, which is nontrivial considering the totally different derivations of these QTSTs; the latter rates are also in reasonable agreement with some other previous results (e.g., obtained via molecular dynamics with quantum transitions), within a factor of approximately 2(7) for the H(D) transfer, thus significantly diminishing the possible range of the exact rates. In addition, it is revealed that a small but nonnegligible inconsistency exists in the parametrization of the Azzouz-Borgis model employed in previous studies, which resulted in the large apparent discrepancy in the calculated rates.