A modification of path integral quantum transition state theory for asymmetric and metastable potentials
A modification of path integral quantum transition state theory for asymmetric and metastable potentials
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DOI：
10.1021/jp992190
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发表时间：
1999-11-25
影响因子：
2.9
通讯作者：
Voth, GA
中科院分区：
文献类型：
--
作者：
Jang, S;Schwieters, CD;Voth, GA
针对不对称 Eckart 势垒和亚稳态势垒，研究了路径积分量子过渡态理论 (PI-QTST) 及其修改版本。对于低温，已证实 PI-QTST 高估了反应速率，其他量子激活速率理论也是如此。然后实施一种简单的校正方法，该方法修改电势的乘积部分，使得其受到电势反应物阱底部能量的限制。对不对称埃卡特势垒和立方亚稳态电位的测试结果表明，该方法可以可靠地估计所考虑的模型系统的反应速率。为了了解通常的 PI-QTST 方法中的误差来源以及校正的基本机制，然后进行详细的半经典分析。该分析表明，Cao 和 Voth 的改良 PI-QTST [Cao, J.； Voth，G.A.J，化学。 Phys, 1996, 105, 6856] 仅当使用经典路径的某个子集时才等效于低温下的半经典弹跳理论。因此得出的结论是，误差源于数值路径积分评估中与乘积束缚态相关的路径的不适当混合。这些乘积路径可以通过建议的校正方法消除，从而使 PI-QTST 对于低温下的强不对称或亚稳态系统更加准确。
Path integral quantum transition state theory (PI-QTST) and its modified versions are studied for an asymmetric Eckart barrier and a metastable potential. For low temperatures, it is confirmed that the PI-QTST overestimates the reaction rate, as do other quantum activated rate theories. A simple correction method which modifies the product part of the potential such that it is bounded by the potential reactant well bottom energy is then implemented. The resulting tests for the asymmetric Eckart barrier and a cubic metastable potential demonstrate that this method gives a reliable estimate of the reaction rate for the model systems considered. For an understanding of the source of the error in the usual PI-QTST method and of the underlying mechanism of the correction, a detailed semiclassical analysis is then performed. This analysis demonstrates that the modified PI-QTST of Cao and Voth [Cao, J.; Voth, G. A. J, Chem. Phys, 1996, 105, 6856] becomes equivalent to the semiclassical bounce theory at low temperature only if a certain subset of classical paths is used. It is therefore concluded that the errors originate from the inappropriate mixing-in of paths associated with the product bound states in numerical path integral evaluations. These product paths are eliminated by the suggested correction method, thus rendering PI-QTST much more accurate for strongly asymmetric or metastable systems at low temperatures.