Azuri Ido, Hirsch Anna, Reilly Anthony M, Tkatchenko Alexandre, Kendler Shai, Hod Oded, Kronik Leeor
Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel.
School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland.
Beilstein J Org Chem. 2018 Feb 9;14:381-388. doi: 10.3762/bjoc.14.26. eCollection 2018.
We present a computational analysis of the terahertz spectra of the monoclinic and the orthorhombic polymorphs of 2,4,6-trinitrotoluene. Very good agreement with experimental data is found when using density functional theory that includes Tkatchenko-Scheffler pair-wise dispersion interactions. Furthermore, we show that for these polymorphs the theoretical results are only weakly affected by many-body dispersion contributions. The absence of dispersion interactions, however, causes sizable shifts in vibrational frequencies and directly affects the spatial character of the vibrational modes. Mode assignment allows for a distinction between the contributions of the monoclinic and orthorhombic polymorphs and shows that modes in the range from 0 to ca. 3.3 THz comprise both inter- and intramolecular vibrations, with the former dominating below ca. 1.5 THz. We also find that intramolecular contributions primarily involve the nitro and methyl groups. Finally, we present a prediction for the terahertz spectrum of 1,3,5-trinitrobenzene, showing that a modest chemical change leads to a markedly different terahertz spectrum.
我们对2,4,6-三硝基甲苯的单斜晶系和正交晶系多晶型物的太赫兹光谱进行了计算分析。当使用包含Tkatchenko-Scheffler成对色散相互作用的密度泛函理论时，发现与实验数据非常吻合。此外，我们表明，对于这些多晶型物，理论结果仅受到多体色散贡献的微弱影响。然而，色散相互作用的缺失会导致振动频率发生相当大的偏移，并直接影响振动模式的空间特征。模式归属有助于区分单斜晶系和正交晶系多晶型物的贡献，结果表明，在0至约3.3太赫兹范围内的模式包含分子间和分子内振动，前者在约1.5太赫兹以下占主导。我们还发现分子内贡献主要涉及硝基和甲基。最后，我们对1,3,5-三硝基苯的太赫兹光谱进行了预测，结果表明适度的化学变化会导致明显不同的太赫兹光谱。
