Ab initio Simulation of Time-Resolved X-ray Spectroscopy

最近开发的用于分子动力学研究的实验X射线光谱学，例如，质子动力学，超快系统间交叉，键离解，激发态弛豫等，提供了在时间尺度上达到飞秒的化学过程的微妙细节的信息。为了充分利用这些研究的潜力，需要理论支持来帮助解释这些新实验并进一步发展。因此，我们的目标是开发和应用最先进的计算方法的基础上，量子力学的时间分辨X射线光谱的全面模拟。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进行建模、预测和支持。除了数学、算法和软件开发之外，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，我们的方法将通过其应用于标准近似往往会崩溃的系统进行测试，即质子/氢转移和非绝热耦合主导的核动力学。详细地说，我们将首先研究LiH和H$_2$O的质子动力学，然后转向吡嗪和苯的非绝热弛豫。最终，我们将研究质子在2-（2 '-羟基苯基）-恶唑（HPO）中的转移，这本身就是一个具有挑战性和吸引力的研究对象。这些应用的难度越来越大，已被选定，使系统的评价开发的方法，以及为了获得有价值的洞察调查光化学过程本身。

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.