In the last two decades, linear-response time-dependent density functional theory (LR-TDDFT) has become one of the most widely used approaches for the computation of the excited-state properties of atoms and molecules. Despite its success in describing the photochemistry and the photophysics of a vast majority of molecular systems, its domain of applicability has been limited by several substantial drawbacks. Commonly identified problems of LR-TDDFT include the correct description of Rydberg states, charge-transfer excited states, doubly excited states, and nearly degenerate states. In addition to these widely recognized shortcomings, the approximate functionals used in LR-TDDFT are unable to fully describe London dispersion interactions. In this work, we aim at understanding the impact of van der Waals interactions on the properties of chemical systems beyond their electronic ground state. For this purpose, we compare the results of excited-state energy profiles and dynamic trajectories for the prototypical cis-stilbene molecule with its 3-3′,5-5′-tetra-tert-butyl derivative. While the explicit treatment of London dispersion interactions results in negligible changes for the cis-stilbene, we show that these attractive forces have a substantial influence on the energetics and structural evolution of the substituted derivative. In the latter case, intramolecular dispersion interactions impact the outcome of the simulation qualitatively, leading to an increased preference for the photocyclization pathway. The methodological consequences of this work are not uniquely applicable to the illustrative stilbene case. In fact, this molecule is representative of a whole class of chemical situations, where dispersion forces dominate the interactions between the unexcited substituents of a photoexcited chromophore. This is, for instance, a common situation in organic photovoltaics where donor molecules are usually functionalized with long alkyl side chains to improve solubility and assembly.

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伦敦色散相互作用如何影响分子开关的光化学过程？

在过去的二十年中，线性响应时间相关的密度泛函理论（LR-TDDFT）已成为计算原子和分子的激发态性质的最广泛使用的方法之一。尽管在描述绝大多数分子系统的光化学和光物理方面取得了成功，但其适用范围却受到一些实质性缺陷的限制。LR-TDDFT的常见问题包括对Rydberg态，电荷转移激发态，双激发态和几乎简并态的正确描述。除了这些公认的缺点外，LR-TDDFT中使用的近似功能无法完全描述伦敦色散相互作用。在这项工作中，我们的目的是了解范德华相互作用对超出电子基态的化学系统性质的影响。为此，我们将激发态能量分布图和动态轨迹的结果作为原型进行比较。顺式-茋分子与其3-3'，5-5'四-叔丁基衍生物。尽管对伦敦色散相互作用的显式处理导致顺式的变化可忽略不计-二苯乙烯，我们表明这些吸引力对取代衍生物的能量学和结构演化有重大影响。在后一种情况下，分子内分散相互作用从质上影响模拟的结果，导致对光环化途径的偏好增加。这项工作的方法学后果并非唯一适用于说明性的二苯乙烯案件。实际上，该分子代表了一整类化学情况，其中分散力主导着光激发发色团的未激发取代基之间的相互作用。例如，这是有机光伏中的常见情况，其中供体分子通常使用长烷基侧链进行官能化以提高溶解性和组装性。