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)光源以前所未有的空间和时间分辨率为观察电子在物质内部的运动开辟了新的途径。通过访问核心能级，x射线脉冲可以区别地询问分子中的不同原子，并且可以以飞秒(十亿分之一秒)或更快的分辨率做到这一点，达到电子在这些系统中运动的自然尺度。这个项目将研究有机分子中一系列依赖时间的关联电子过程，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程序包来模拟X射线和分子之间的相互作用。虽然只是理论上的，但这个项目的目标是确定可用于测量的过程和可观测对象，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以及通过培训本科生和研究生级别的初级研究人员来开发人力资源来服务于国家利益。PI和他的小组将研究分子与X射线之间的相互作用，作为触发和观察这些系统中依赖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，一个是常规地模拟有机分子中可以用X射线诱导和/或探测的一系列相关过程。为此，模拟将使用多参考完全或受限活性空间形式主义(MR-CAS/RAS)中的电子关联的显式处理，使用密度泛函理论或以其他方式优化的分子轨道来改善MR-CAS/RAS的收敛。该项目的另一个目标将是将在这些模拟中观察到的相关动力学和过程，即波函数，与实验可访问的可观测对象唯一地联系起来。这个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计划和既定的刺激竞争研究计划(EPSCoR)联合资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.