We demonstrate that electronic excitations and their transition densities can be obtained from real-time density functional theory calculations with great accuracy by relating the data from numerical propagation to the analytical form of the electronic response after a boost excitation. The latter is derived in this article. This approach facilitates quantitatively obtaining oscillator strengths, identifying excitations that carry very small oscillator strengths, and assessing electronic couplings from transition densities based on comparatively short propagation times. These features are of interest in particular for studying light-harvesting systems. For demonstration purposes, we study the Q band excitations of bacteriochlorophyll a (BChla) and calculate coupling strengths between two BChla’s to check the validity of the dipole–dipole and pure Coulomb coupling mechanisms. For further illustration, we investigate the paradigm test system Na₄ and the coupling between two Na₂ dimers.

中文翻译：

---

实时密度泛函理论的准确评估，为具有挑战性的电子动力学提供了途径

我们证明，通过将数值传播的数据与升压激励后的电子响应的解析形式相关联，可以从实时密度泛函理论计算中获得非常高精度的电子激励及其跃迁密度。后者是从本文衍生而来的。这种方法有助于定量获得振荡器强度，识别携带非常小的振荡器强度的激励，并基于相对较短的传播时间从跃迁密度评估电子耦合。这些特征尤其对于研究光收集系统很重要。为了演示的目的，我们研究了细菌叶绿素a（BChl a）并计算两个BChl a之间的耦合强度，以检查偶极–偶极和纯库仑耦合机制的有效性。为了进一步说明，我们研究了范式测试系统Na ₄和两个Na ₂二聚体之间的偶联。