A specific method, combining some ingredients of the well-known DDA and PDI approaches, has been developed in our group since many years to calculate the absorption cross-sections of carbonaceous nanoparticles based on their atomistic details. This method, here named the Dynamic Atomic Dipole Interaction (DADI) model, requires the knowledge of the position and frequency-dependent polarizability of each atom constituting the nanoparticles. While the atomic positions can be quite easily obtained, for example as the results of molecular dynamics simulations, obtaining the frequency-dependent atomic polarizabilities is a trickier task. Here, a fitting procedure, named the reverse-DADI method, has been applied to calculate the frequency-dependent atomic polarizability values for carbon and hydrogen atoms involved in aromatic cycles or in aliphatic chains, on the basis of frequency-dependent molecular polarizabilities of various PAH and alkane molecules, calculated with the TD-DFT theory, in the UV–Visible range. Then, using these frequency-dependent atomic polarizabilities as input parameters in the DADI model has been shown to lead to an accurate representation of the absorption cross-sections of various PAH and alkane molecules with respect to the corresponding values obtained at the TD-DFT level, with however the great advantage of a much shorter time of calculations. Furthermore, these results are indications of a good transferability of the frequency-dependent atomic polarizability values obtained here to any C or H atom of any PAH or alkane molecule. This opens the way for building large databases of optical properties for carbonaceous species of atmospheric or astrophysical interests.

中文翻译：

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反向 DADI 方法：计算碳氢化合物结构中碳原子和氢原子的频率相关原子极化率


多年来，我们小组开发了一种特定的方法，结合了著名的 DDA 和 PDI 方法的一些成分，以根据碳质纳米颗粒的原子细节计算其吸收截面。这种方法，这里称为动态原子偶极子相互作用 （DADI） 模型，需要了解构成纳米粒子的每个原子的位置和频率相关极化率。虽然原子位置可以很容易地获得，例如作为分子动力学模拟的结果，但获得与频率相关的原子极化率是一项更棘手的任务。在这里，应用了一种称为反向 DADI 方法的拟合程序，以计算芳香族循环或脂肪链中涉及的碳和氢原子的频率相关原子极化率值，基于各种 PAH 和烷烃分子的频率相关分子极化率，使用 TD-DFT 理论计算，在紫外-可见光范围内。然后，使用这些与频率相关的原子极化率作为 DADI 模型中的输入参数已被证明可以准确表示各种 PAH 和烷烃分子的吸收截面相对于在 TD-DFT 水平获得的相应值，但具有计算时间更短的巨大优势。此外，这些结果表明，此处获得的频率相关原子极化率值具有良好的可转移性，可转移到任何 PAH 或烷烃分子的任何 C 或 H 原子。这为为大气或天体物理学感兴趣的碳质物种构建大型光学特性数据库开辟了道路。