Theory of Dynamical Correlated-Electron Processes in Molecules Induced and Probed with x-Ray Light

X射线自由电子激光（XFEL）光源正在开辟以前所未有的空间和时间分辨率观察物质内部电子运动的途径。通过进入核心能级，X射线脉冲可以有区别地询问分子中的不同原子，并且它们可以以飞秒（十亿分之一秒的百万分之一）或更快的分辨率这样做，达到电子在这些系统中移动的自然尺度。这个项目将研究一系列与时间相关的相关电子过程，这些过程可以用x射线诱导和探测。为此，PI和他的团队将利用现有的量子化学包来模拟X射线和分子之间的相互作用。虽然是理论上的，但该项目的目标是确定可用于测量的过程和可观测量，最终目标是与XFEL实验活动合作。该项目将通过促进X射线分子科学的发展和通过培养本科生和研究生水平的初级研究人员来开发人力资源，为国家利益服务。PI及其团队将研究分子与X射线光之间的相互作用，作为触发和观察这些系统中依赖于时间的相关过程的工具，重点是核心电子。在两个主要目标中，一个是常规模拟一系列可以用X射线诱导和/或探测的有机分子中的相关过程。为此，模拟将使用多参考完全或限制活性空间形式主义（MR-CAS/RAS）中的电子相关的显式处理，使用密度泛函理论或以其他方式优化的分子轨道，以改善MR-CAS/RAS的收敛性。该项目的另一个目标是将这些模拟中观察到的相关动力学和过程独特地联系起来，即，波函数，到实验中可以得到的观测值。该项目还将研究用真实的XFEL脉冲模拟光物质相互作用的一些实际方面。该项目由原子，分子，和光学物理理论程序和既定的程序，以刺激竞争力的研究（EPSCoR）该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查进行评估，被认为值得支持的搜索.

X-ray free-electron laser (XFEL) light sources are opening avenues to observe the motion of electrons inside matter with unprecedented space and time resolution. By accessing core levels, x-ray pulses can discriminatively interrogate different atoms in molecules, and they can do so with femtosecond (one millionth of a billionth of a second) resolution or faster, reaching the natural scales at which electrons move in these systems. This project will study a range of time-dependent correlated-electron processes in organic molecules that can be induced and probed with x-rays. To do so, the PI and his group will leverage existing quantum-chemistry packages to simulate the interaction between x-rays and molecules. While theoretical, this project will aim to identify processes and observables that are accessible to measurements, with the ultimate objective to collaborate with XFEL experimental campaigns. The project will serve the national interest through the advancement of x-ray-enabled molecular science and through the development of human resources via the training of junior researchers at the undergraduate and graduate levels.The PI and his group will study the interactions between molecules and x-ray light, as the vehicle for triggering and observing time-dependent correlated processes in these systems, with an emphasis on core electrons. Of the two main objectives, one will be to routinely simulate a range of correlated processes in organic molecules that can be induced and/or probed with x-rays. To do so, simulations will use an explicit treatment of electron correlation in a multi-reference complete- or restricted-active space formal-ism (MR-CAS/RAS) using density-functional-theory, or otherwise optimized, molecular orbitals to improve the convergence of the MR-CAS/RAS. An additional objective of the project will be to uniquely connect the correlated dynamics and processes observed in these simulations, i.e., the wave functions, to observables that are accessible to experiments. This project will also investigate some of the practical aspects of modeling light-matter interactions with realistic XFEL pulses.This project is jointly funded by the Atomic, Molecular, and Optical Physics Theory Program and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.