We present a first-principles model that partitions Raman intensities to atomic and bond contributions. This framework allows us to interpret the chemical mechanism in surface-enhanced Raman scattering (SERS) as interatom charge flow modulations, which we define as Raman bonds. Hirshfeld partitioning and charge density localization are applied to express polarizability derivatives as charge flow modulations. Model systems consisting of pyridines, thiols, and carbenes interacting with metal clusters are studied using time-dependent density functional theory. We demonstrate that the mode-specific enhancements can be explained as Raman bonds conjugated across the molecule-metal interface. We also illustrate that the changes in Raman intensities induced by electric fields or chemical substitutions can generally be interpreted as changes of charge flows. The model is shown to work consistently for different types of molecule-metal bonds. Furthermore, our work shows that increasing the Raman bond conjugation across the interface leads to stronger chemical enhancements. The Raman bond model developed in this work provides a quantitative and intuitive interpretation of the chemical mechanism in SERS.

中文翻译：

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使用拉曼键模型解释SERS中的化学机理。

我们提出了将拉曼强度划分为原子和键贡献的第一原理模型。该框架使我们能够将表面增强拉曼散射（SERS）中的化学机理解释为原子间电荷流调制，我们将其定义为拉曼键。应用Hirshfeld划分和电荷密度局部化将极化率导数表示为电荷流调制。使用与时间有关的密度泛函理论研究了由吡啶，硫醇和羧甲基与金属簇相互作用组成的模型系统。我们证明，特定于模式的增强可以解释为跨分子-金属界面共轭的拉曼键。我们还说明，由电场或化学取代引起的拉曼强度变化通常可以解释为电荷流的变化。该模型显示出对不同类型的分子-金属键始终有效。此外，我们的工作表明，增加界面上的拉曼键共轭可增强化学作用。在这项工作中开发的拉曼键模型为SERS中的化学机理提供了定量和直观的解释。