High-Resolution THz Spectroscopy and Solid-State Density Functional Theory Calculations of Polycyclic Aromatic Hydrocarb
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High-Resolution THz Spectroscopy and Solid-State Density Functional Theory Calculations of Polycyclic Aromatic Hydrocarbons Feng Zhang 1 & Houng-Wei Wang 2 & Keisuke Tominaga 1 Tetsuo Sasaki 3
2
& Michitoshi Hayashi &
Received: 30 April 2019 / Accepted: 25 August 2019/ # Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract High-resolution and broadband THz spectra of the crystals of nine polycyclic aromatic hydrocarbons (PAHs) are presented. Five PAHs are comprised of ortho-fused benzene rings and the other four of peri-fused benzene rings. THz mode assignment is performed by using the anthracene and pyrene crystals as examples. The performance of the PBE functional augmented by Grimme’s two dispersion correction terms, D* and D3, respectively, are rigorously evaluated against the experimental criteria of frequency and isotope shift (IS). The D* and D3 terms use empirical and semi-classical approach for correcting the Londontype dispersion interactions, respectively. The nature of each THz mode simulated by PBE-D* and that by PBE-D3 is quantitatively compared in terms of the percentage contributions of the intermolecular and the intramolecular vibrations to the vibrational energy. We find that the two methods have equivalent performance in reproducing the frequencies, ISs, and nature of THz modes of both the anthracene and pyrene crystals. Keywords Terahertz spectroscopy . Phonon mode . Solid-state density functional theory . London dispersion force . Isotope shift
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10762-01900621-0) contains supplementary material, which is available to authorized users.
* Keisuke Tominaga [email protected] * Michitoshi Hayashi [email protected]
1
Molecular Photoscience Research Center, Kobe University, Nada, Kobe 657-0013, Japan
2
Center for Condensed Matter Sciences, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei 10617, Taiwan
3
Research Institute of Electronics, Shizuoka University, Hamamatsu, Shizuoka 432-8011, Japan
Journal of Infrared, Millimeter, and Terahertz Waves
1 Introduction The past two decades have witnessed huge growth of THz techniques in a variety of application fields such as sensing, chemical analysis, and imaging [1–10]. The study of interactions between THz radiation and matter is of central importance for retrieving useful information from and exploring the maximum value of the experimental data. From the spectroscopic point of view, THz radiation bridges the two frequency regions where the dielectric relaxation and localized vibrations of molecules and atoms dominate; the THz band accommodates the high-energy tail of the dielectric relaxation and delocalized vibrations which feature the collective motions of molecules and atoms via intermolecular interactions. This feature is particularly important for interpreting the molecular dynamics in the THz frequency region of liquids [11–13], hydrated macromolecules [14, 15], and amorphous solids [16–18]. In a molecular
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