Schmalz Felix, Kopp Wassja A, Kröger Leif C, Leonhard Kai
Chair of Technical Thermodynamics, RWTH Aachen University, Aachen 52062, Germany.
ACS Omega. 2020 Jan 31;5(5):2242-2253. doi: 10.1021/acsomega.9b03383. eCollection 2020 Feb 11.
Anharmonicity can greatly affect rate constants. One or even several orders of magnitude of deviation are found for obtaining rate constants using the standard rigid-rotor harmonic-oscillator model. In turn, reactive molecular dynamics (MD) simulations are a powerful way to explore chemical reaction networks and calculate rate constants from the fully anharmonic potential energy surface. However, the classical nature of the dynamics and the required numerical efficiency of the force field limit the accuracy of the resulting kinetics. We combine the best of both worlds by presenting an approximation that pairs anharmonic information intrinsic to classical MD with high-accuracy energies and frequencies from quantum-mechanical electronic structure calculations. The proposed scheme is applied to hydrogen abstractions in the methane system, which allows for the benchmarking of rate constants corrected by our approach against experimental rate constants. This comparison reveals a standard deviation of factor 2.6. Two archetypes of possible failure are identified in the course of a detailed investigation of the CH + H → CH + H reaction. From this follows the application range of the method, within which the method shows a standard deviation of factor 2.1. The computational efficiency and beneficial scaling of the method allow for application to larger systems, as shown for hydrogen abstraction from 2-butanone by HO .
非谐性会极大地影响速率常数。使用标准的刚性转子-简谐振子模型来获得速率常数时，会发现有一个甚至几个数量级的偏差。反过来，反应分子动力学（MD）模拟是探索化学反应网络并从完全非谐势能面计算速率常数的有力方法。然而，动力学的经典性质以及力场所需的数值效率限制了所得动力学的准确性。我们通过提出一种近似方法将两者的优点结合起来，该近似方法将经典MD固有的非谐信息与量子力学电子结构计算得到的高精度能量和频率配对。所提出的方案应用于甲烷系统中的氢提取，这使得可以将我们方法校正后的速率常数与实验速率常数进行基准比较。这种比较显示出2.6倍的标准偏差。在对CH + H → CH + H反应的详细研究过程中，确定了两种可能失败的原型。由此得出该方法的应用范围，在此范围内该方法显示出2.1倍的标准偏差。该方法的计算效率和良好的标度性允许应用于更大的系统，如HO从2-丁酮中提取氢的情况所示。
