Prlj Antonio, Hollas Daniel, Curchod Basile F E
Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K.
Division of Physical Chemistry, Ruđer Bošković Institute, Zagreb 10000, Croatia.
J Phys Chem A. 2023 Sep 7;127(35):7400-7409. doi: 10.1021/acs.jpca.3c02333. Epub 2023 Aug 9.
Nonadiabatic molecular dynamics offers a powerful tool for studying the photochemistry of molecular systems. Key to any nonadiabatic molecular dynamics simulation is the definition of its (ICs), ideally representing the initial molecular quantum state of the system of interest. In this work, we provide a detailed analysis of how ICs may influence the calculation of experimental observables by focusing on the photochemistry of methylhydroperoxide (MHP), the simplest and most abundant organic peroxide in our atmosphere. We investigate the outcome of trajectory surface hopping simulations for distinct sets of ICs sampled from different approximate quantum distributions, namely harmonic Wigner functions and ab initio molecular dynamics using a quantum thermostat (QT). Calculating photoabsorption cross-sections, quantum yields, and translational kinetic energy maps from the results of these simulations reveals the significant effect of the ICs, in particular when low-frequency (∼ a few hundred cm) normal modes are connected to the photophysics of the molecule. Overall, our results indicate that sampling ICs from ab initio molecular dynamics using a QT is preferable for flexible molecules with photoactive low-frequency modes. From a photochemical perspective, our nonadiabatic dynamics simulations offer an explanation for a low-energy tail observed at high excitation energy in the translational kinetic energy map of MHP.
非绝热分子动力学为研究分子体系的光化学提供了一个强大的工具。任何非绝热分子动力学模拟的关键在于其初始条件（ICs）的定义，理想情况下，这些初始条件代表了感兴趣体系的初始分子量子态。在这项工作中，我们通过聚焦于大气中最简单且最丰富的有机过氧化物——甲基过氧化氢（MHP）的光化学，详细分析了初始条件如何影响实验可观测量的计算。我们研究了从不同近似量子分布（即谐振维格纳函数和使用量子恒温器（QT）的从头算分子动力学）中采样得到的不同初始条件集的轨迹表面跳跃模拟结果。从这些模拟结果计算光吸收截面、量子产率和平动能图谱，揭示了初始条件的显著影响，特别是当低频（约几百厘米）正则模与分子的光物理过程相关联时。总体而言，我们的结果表明，对于具有光活性低频模式的柔性分子，使用QT从从头算分子动力学中采样初始条件更为可取。从光化学角度来看，我们的非绝热动力学模拟为MHP平动能图谱在高激发能下观察到的低能尾部提供了解释。
