In this Perspective we show that semiclassical methods provide a rigorous hierarchical way to study the vibrational spectroscopy and kinetics of complex molecular systems. The time averaged approach to spectroscopy and the semiclassical transition state theory for kinetics, which have been first adopted and then further developed in our group, provide accurate quantum results on rigorous physical grounds and can be applied even when dealing with a large number of degrees of freedom. In spectroscopy, the multiple coherent, divide-and-conquer, and adiabatically switched semiclassical approaches have practically permitted overcoming issues related to the convergence of results. In this Perspective we demonstrate the possibility of studying the semiclassical vibrational spectroscopy of a molecule adsorbed on an anatase (101) surface, a system made of 51 atoms. In kinetics, the semiclassical transition state theory is able to account for anharmonicity and the coupling between the reactive and bound modes. Our group has developed this technique for practical applications involving the study of phenomena like kinetic isotope effect, heavy atom tunneling, and elusive conformer lifetimes. Here, we show that our multidimensional anharmonic quantum approach is able to tackle on-the-fly the thermal kinetic rate constant of a 135 degree-of-freedom system. Overall, semiclassical methods open up the possibility to describe at the quantum mechanical level systems characterized by hundreds of degrees of freedom leading to the accurate spectroscopic and kinetic description of biomolecules and complex molecular systems.

中文翻译：

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用半经典方法研究复杂分子系统的光谱学和动力学的观点


在本视角中，我们表明半经典方法提供了一种严格的分层方法来研究复杂分子系统的振动光谱和动力学。我们小组首先采用并进一步发展了光谱学的时间平均方法和动力学的半经典过渡态理论，它们在严格的物理基础上提供了准确的量子结果，甚至可以在处理大量度数时应用。自由。在光谱学中，多重相干、分而治之和绝热切换的半经典方法实际上可以克服与结果收敛相关的问题。在本视角中，我们展示了研究吸附在锐钛矿 (101) 表面（由 51 个原子组成的系统）上的分子的半经典振动光谱的可能性。在动力学中，半经典过渡态理论能够解释非调和性以及反应模式和束缚模式之间的耦合。我们的小组开发了这项技术，用于实际应用，涉及动力学同位素效应、重原子隧道效应和难以捉摸的构象异构体寿命等现象的研究。在这里，我们展示了我们的多维非谐量子方法能够实时处理 135 自由度系统的热动力学速率常数。总体而言，半经典方法开辟了在量子力学水平上描述具有数百个自由度的系统的可能性，从而可以对生物分子和复杂分子系统进行准确的光谱和动力学描述。