First Principles Simulations of Soft X-ray Spectroscopy of Molecular Charge and Energy Transfer Processes

分子电荷和能量转移过程软 X 射线光谱的第一原理模拟

• 批准号: 252105138
• 负责人: Professor Dr. Oliver Kühn
• 金额: --
• 依托单位: Arbeitsgruppe Molekulare Quantendynamik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/252105138?language=en
• 关键词: First; Principles; Simulations; Soft; ray

The overarching goal of this project is the development and numerical implementation of theoretical methods for the description of the soft X-ray spectroscopy of molecular energy and charge transfer. Energy and charge transfer involving valence excitations are ubiquitous processes in novel solar energy materials used as photocatalysts or in organic photovoltaics. Here, future performance improvements will benefit from an in-depth mechanistic understanding on the molecular scale. Moreover, performance limitations due to classical Physics might be overcome by making use of nontrivial quantum effects as a working principle. Common characterization of these processes employing optical detection often faces the challenge of congested spectra, which are difficult to assign unambiguously. In contrast, X-ray spectroscopy is element specific such that individual atoms of a molecular complex can be addressed by means of their absorption edges. Large scale facilities but also table top soft X-ray sources are becoming increasingly available in this rapidly developing field, demanding for adequate theoretical developments. While the investigation of compounds containing a single transition metal center with, for instance, optical pump and X-ray probe techniques is becoming standard nowadays, respective studies of systems with multiple metal centers are still rare. In particular first principles theory faces its limits when it comes to the important L-edges since their spectra are shaped by multiconfigurational and spin-orbit coupling effects. This project will follow a new strategy to cope with this situation. Making use of the local nature of X-ray absorption, multichromophoric complexes will be described in terms of interacting fragments. The idea is borrowed from Frenkel exciton theory, which is well-established in the context of valence excitations. Application to valence and core excited states of multichromophoric complexes will provide a unifying frame for the description of the X-ray spectroscopy of optically triggered valence state dynamics. Two types of applications will be considered. First, in a proof-of-principle study bimetallic compounds will be considered, thus extending the scope of the original proposal. Second, energy transfer and interfacial charge separation in model systems for organic photovoltaics will be investigated in close cooperation with experiment. Particular emphasis will be paid to unravel the signatures of exciton wave packet coherence and delocalization, which shall give a new twist to an ongoing debate in this field.

该项目的首要目标是发展和数值实现的理论方法的描述的软X射线光谱的分子能量和电荷转移。涉及价态激发的能量和电荷转移在用作光催化剂的新型太阳能材料或有机光催化剂中普遍存在。在这里，未来的性能改进将受益于对分子尺度的深入机理理解。此外，由于经典物理学的性能限制可以通过使用非平凡的量子效应作为工作原理来克服。采用光学检测的这些过程的共同表征通常面临拥挤光谱的挑战，这是难以明确分配的。相比之下，X射线光谱是元素特异性的，使得分子复合物的单个原子可以通过它们的吸收边来寻址。在这个快速发展的领域，大规模的设施，但也桌面软X射线源变得越来越可用，需要足够的理论发展。虽然目前使用例如光泵浦和X射线探针技术对含有单个过渡金属中心的化合物的研究已经成为标准，但是对具有多个金属中心的系统的相应研究仍然很少。特别是第一性原理理论面临着它的局限性，当它涉及到重要的L-边缘，因为他们的光谱形状的多组态和自旋轨道耦合效应。该项目将采取新的战略来科普这种情况。利用X射线吸收的局部性质，将根据相互作用的碎片来描述多发色团复合物。这个想法借用了弗伦克尔激子理论，该理论在价激发的背景下已经得到了充分的认可。应用于多发色团络合物的价态和核心激发态将为描述光触发价态动力学的X射线光谱提供统一的框架。将考虑两种类型的应用程序。首先，在一项原理证明研究中，将考虑使用非线性化合物，从而扩大原提案的范围。其次，将与实验密切合作，研究有机光化学模型体系中的能量传递和界面电荷分离。特别强调将解开激子波包相干性和离域的签名，这将给一个新的转折正在进行的辩论在这一领域。