Ab initio Simulation of Time-Resolved X-ray Spectroscopy

最近发展起来的用于分子动力学研究的实验X射线光谱仪，例如质子动力学、超快系间交叉、键解离、激发态弛豫等，提供了精确到飞秒级的时间尺度上化学过程的精细细节的信息。为了充分利用这类研究的潜力，需要理论支持来帮助解释和进一步发展这些新颖的实验。因此，我们的目标是开发和应用基于量子力学的最先进的计算方法，用于时间分辨X射线能谱的综合模拟。最终，我们将提供一个计算工具箱，用于非专家对这些新颖的时间分辨实验的建模、预测和支持。除了这一数学、算法和软件开发，我们还将挑战广泛使用的假设，例如洛伦兹近似，并将量子动力学模拟的使用与经典表面跳跃动力学进行比较。与此同时，我们将对我们开发的方法进行基准测试，通过连续降低准确性来采用可理解的策略。因此，我们的方法将通过将它们应用于标准近似趋于崩溃的系统来检验，即质子/氢转移和由非绝热耦合主导的核动力学。详细地，我们将研究LiH和H$2$O的质子动力学，然后转向在吡嗪和苯中的非绝热驰豫。最后，我们将研究2-(2‘-羟基苯基)恶唑(HPO)中的质子转移，这本身就是一个具有挑战性和吸引力的研究对象。选择这些难度越来越大的应用是为了能够对所开发的方法进行系统评估，以及对所研究的光化学过程本身获得有价值的见解。

Recent developed experimental X-ray spectroscopies for the investigation of molecular dynamics, for example, proton dynamics, ultrafast intersystem crossing, bond dissociation, excited-state relaxation, and more, provide information on subtle details of chemical processes on a time-scale reaching down to femtoseconds. To leverage the full potential of such studies, theoretical support is required to help these novel experiments to be interpreted and to be developed further. We thus aim at developing and applying state-of-the-art computational methods based on quantum mechanics for the comprehensive simulation of time-resolved X-ray spectroscopies. Eventually, we will provide a computational toolbox for modeling, prediction, and support of these novel time-resolved experiments by non-experts.Besides this mathematical, algorithmic, and software development, we will challenge widely employed assumptions like for example the Lorentzian approximation and compare the use of quantum dynamical simulations with classical surface hopping dynamics. Concomitantly, we will benchmark our developed methodologies, employing a comprehensible strategy by successively reducing the accuracy. Our methods will thereby be tested by their application to systems in which the standard approximations tend to break down, i.e. proton/hydrogen transfer and nuclear dynamics dominated by non-adiabatic couplings. In detail, we will study the proton dynamics of LiH and H$_2$O as initial tests, then turn to non-adiabatic relaxation in pyrazine and benzene. Eventually, we will study proton transfer in 2-(2'-hydroxyphenyl)-oxazole (HPO), which is a challenging and fascinating research object itself. These applications of increasing difficulty have been selected to enable a systematic evaluation of the developed methods, as well as in order to obtain valuable insight into the investigated photochemical processes themselves.