Abstract-First-Principles Calculation of Terahertz Absorption with Dispersion Correction of 2,2′-Bithiophene as Model Compound

Jongtaek Kim †‡, O-Pil Kwon §, Mojca Jazbinsek ∥, Young Choon Park †, and Yoon Sup Lee *†

† Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea

‡ Department of Basic Science, Korea Air Force Academy (KAFA), Cheongju 363-849, Korea

§ Department of Molecular Science and Technology, Ajou University, Suwon 443-749, Korea

∥ Institute of Computational Physics, Zurich University of Applied Sciences (ZHAW), 8401 Winterthur,Switzerland

J. Phys. Chem. C, Article ASAP

DOI: 10.1021/acs.jpcc.5b02661

Publication Date (Web): May 15, 2015

Copyright © 2015 American Chemical Society

*E-mail: yslee@kaist.edu. Tel.: +82-42-350-2821.

Terahertz absorption of organic materials is closely linked to molecular arrangements and their intermolecular interactions and is important for material identification as well as THz generation. Theoretical calculations of solid-state vibrations known as phonons help to understand intermolecular interactions responsible for THz absorption but frequently are of limited use without considering dispersion interaction. In this study, we have calculated the THz phonon modes of an organic model crystal 2,2′-bithiophene, considering dispersion intermolecular interactions assuming the fixed cell dimensions. Both energies and intensities of phonon modes at low frequencies were interpreted concentrating on the intermolecular level in conjunction with hydrogen bonds and showed an excellent agreement with the experimental results. This approach to identify the phonon modes responsible for strong THz absorptions and to interpret those modes in terms of intermolecular vibrations is also expected to be applicable to the field of THz generation using nonlinear optical organic crystals.