Calculation of Electron Ionization Mass Spectra with Semiempirical GFNn-xTB Methods

In this work, we have tested two different extended tight-binding methods in the framework of the quantum chemistry electron ionization mass spectrometry (QCEIMS) program to calculate electron ionization mass spectra. The QCEIMS approach provides reasonable, first-principles computed spectra, which can be directly compared to experiment. Furthermore, it provides detailed insight into the reaction mechanisms of mass spectrometry experiments. It sheds light upon the complicated fragmentation procedures of bond breakage and structural rearrangements that are difficult to derive otherwise. The required accuracy and computational demands for successful reproduction of a mass spectrum in relation to the underlying quantum chemical method are discussed. To validate the new GFN2-xTB approach, we conduct simulations for 15 organic, transition-metal, and main-group inorganic systems. Major fragmentation patterns are analyzed, and the entire calculated spectra are directly compared to experimental data taken from the literature. We discuss the computational costs and the robustness (outliers) of several calculation protocols presented. Overall, the new, theoretically more sophisticated semiempirical method GFN2-xTB performs well and robustly for a wide range of organic, inorganic, and organometallic systems.本研究依托量子化学电子电离质谱（quantum chemistry electron ionization mass spectrometry, QCEIMS）程序框架，测试了两种不同的扩展紧束缚方法，以计算电子电离质谱。QCEIMS方法可生成合理的第一性原理计算质谱，可直接与实验实测谱图进行比对。此外，该方法还可为质谱实验的反应机理提供详细的解析视角，阐明此前难以通过其他手段推导的键断裂与结构重排等复杂碎裂过程。本研究探讨了成功复刻质谱所需的精度与计算资源需求，及其与底层量子化学方法的关联。为验证新型GFN2-xTB方法的可靠性，我们针对15种有机体系、过渡金属体系及主族无机体系开展了模拟计算。研究对主要碎裂模式进行了分析，并将全部计算得到的质谱与文献中的实验数据直接进行比对。本研究还讨论了多种计算方案的计算成本与鲁棒性（异常值情况）。总体而言，这种理论层面更为精密的新型半经验方法GFN2-xTB，可在有机、无机及有机金属等广泛体系中实现优异且稳定的计算表现。