School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia.
School of Chemistry, The University of New South Wales, Sydney, NSW 2052, Australia.
J Chem Phys. 2018 May 21;148(19):194113. doi: 10.1063/1.5023508.
A new approach for preventing zero-point energy (ZPE) violation in quasi-classical trajectory (QCT) simulations is presented and applied to HCO "roaming" reactions. Zero-point energy may be problematic in roaming reactions because they occur at or near bond dissociation thresholds and these channels may be incorrectly open or closed depending on if, or how, ZPE has been treated. Here we run QCT simulations on a "ZPE-corrected" potential energy surface defined as the sum of the molecular potential energy surface (PES) and the global harmonic ZPE surface. Five different harmonic ZPE estimates are examined with four, on average, giving values within 4 kJ/mol-chemical accuracy-for HCO. The local harmonic ZPE, at arbitrary molecular configurations, is subsequently defined in terms of "projected" Cartesian coordinates and a global ZPE "surface" is constructed using Shepard interpolation. This, combined with a second-order modified Shepard interpolated PES, , allows us to construct a proof-of-concept ZPE-corrected PES for HCO, , at no additional computational cost to the PES itself. Both and are used to model product state distributions from the H + HCO → H + CO abstraction reaction, which are shown to reproduce the literature roaming product state distributions. Our ZPE-corrected PES allows all trajectories to be analysed, whereas, in previous simulations, a significant proportion was discarded because of ZPE violation. We find ZPE has little effect on product rotational distributions, validating previous QCT simulations. Running trajectories on , however, shifts the product kinetic energy release to higher energy than on and classical simulations of kinetic energy release should therefore be viewed with caution.
提出了一种防止准经典轨迹(QCT)模拟中零点能(ZPE)违反的新方法，并将其应用于 HCO“漫游”反应。在漫游反应中，零点能可能是一个问题，因为它们发生在或接近键离解阈值，并且这些通道可能会不正确地打开或关闭，具体取决于是否以及如何处理 ZPE。在这里，我们在一个“ZPE 校正”势能面上运行 QCT 模拟，该势能面定义为分子势能面(PES)和全局谐波 ZPE 面的总和。我们检查了五种不同的谐波 ZPE 估计，其中四种平均在 4 kJ/mol-化学精度范围内给出了 HCO 的值。随后，根据“投影”笛卡尔坐标定义了任意分子构型的局部谐波 ZPE，并使用 Shepard 插值构建了全局 ZPE“表面”。这与二阶修正的 Shepard 插值 PES 相结合，允许我们构建 HCO 的概念验证 ZPE 校正 PES， ，而不会对 PES 本身增加额外的计算成本。 和 都用于模拟 H + HCO → H + CO 抽取反应的产物态分布，结果表明它们再现了文献中的漫游产物态分布。我们的 ZPE 校正 PES 允许分析所有轨迹，而在以前的模拟中，由于 ZPE 违反，大量轨迹被丢弃。我们发现 ZPE 对产物转动分布几乎没有影响，验证了以前的 QCT 模拟。然而，在 上运行轨迹会将产物动能释放转移到比 上更高的能量，因此应该谨慎看待基于经典模拟的动能释放。
