Ab initio Simulation of Time-Resolved X-ray Spectroscopy

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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.