Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie der Universität Bonn, Beringstr. 4, Bonn D-53115, Germany.
J Chem Theory Comput. 2020 Dec 8;16(12):7709-7720. doi: 10.1021/acs.jctc.0c00990. Epub 2020 Nov 17.
Interpreting response properties such as the polarizability, optical rotation (OR), or hyperpolarizabilities is a complex task for which a uniform strategy would be desirable. We propose a response analysis procedure called the RespA approach with two interrelated schemes to describe molecular optical response properties in terms of natural response orbitals (NROs) and chemical fragment response for convenient elucidation of structure-(optical)property relationships. These quantities can be easily extracted from the frequency-dependent perturbed one-electron transition/current density matrix obtained from any quantum mechanical response function calculation. NROs provide the most compact representation of the virtual excitations occurring in the (hyper)scattering process. It is decomposed in hole and electron NRO pairs providing a simple exciton picture. For a chemist, it is natural to interpret a property by decomposing it into functional groups or fragment contributions. In this spirit, the response is partitioned into on-site and between-site fragment responses, allowing a property mapping into real space. The new RespA procedure was implemented and tested at the simplified time-dependent density functional theory (sTD-DFT) level enabling calculations for large systems. The RespA strategy is a method-independent route for the understanding of a wide variety of response properties. We showcase how the chemically intuitive RespA approach extracts easily structure-property relationships for the particularly difficult case of OR. As examples, we demonstrate how to enhance the OR of [5]helicene and norbornenone, provide an analysis of the change of the OR observed for camphor and fenchone, and finally investigate the case of a (,)-bis-helicenic 2,2'-bipyridine chiroptical switch.
解释分子的极化率、旋光性（OR）或超极化率等响应性质是一项复杂的任务，理想情况下需要采用统一的策略。我们提出了一种称为 RespA 的响应分析方法，该方法有两个相互关联的方案，用于根据自然响应轨道（NRO）和化学片段响应来描述分子的光学响应性质，以便于阐明结构-（光学）性质关系。这些量可以从任何量子力学响应函数计算中获得的频域受扰单电子跃迁/电流密度矩阵中轻松提取。NRO 提供了（超）散射过程中虚拟激发的最紧凑表示。它分解为孔和电子 NRO 对，提供了一个简单的激子图像。对于化学家来说，通过将性质分解为官能团或片段贡献来解释性质是很自然的。本着这种精神，将响应分为局域和局间片段响应，允许将性质映射到实空间。新的 RespA 程序在简化的时间相关密度泛函理论（sTD-DFT）水平上实现并进行了测试，从而能够对大型系统进行计算。RespA 策略是一种独立于方法的途径，可以理解各种响应性质。我们展示了化学上直观的 RespA 方法如何轻松提取旋光性的结构-性质关系，这对于旋光性特别困难的情况尤其有用。作为示例，我们演示了如何增强[5]螺旋烯和降冰片酮的旋光性，分析了樟脑和葑酮观察到的旋光性变化，并最终研究了（，）-双螺旋烯 2,2'-联吡啶手性光开关的情况。
