Understanding the fundamental processes of light-matter interaction is important for detection of explosives and other energetic materials, which are active in the infrared and terahertz (THz) region. We report a comprehensive study on electronic and vibrational lattice properties of structurally similar 1,3-dinitrobenzene (1,3- DNB) crystals through first-principles electronic structure calculations and THz spectroscopy measurements on polycrystalline samples. Starting from reported x-ray crystal structures, we use density-functional theory (DFT) with periodic boundary conditions to optimize the structures and perform linear response calculations of the vibrational properties at zero phonon momentum. The theoretically identified normal modes agree qualitatively with those obtained experimentally in a frequency range up to 2.5 THz and quantitatively at much higher frequencies. The latter frequencies are set by intra-molecular forces. Our results suggest that van der Waals dispersion forces need to be included to improve the agreement between theory and experiment in the THz region, which is dominated by intermolecular modes and sensitive to details in the DFT calculation. An improved comparison is needed to assess and distinguish between intra- and intermolecular vibrational modes characteristic of energetic materials.
Terahertz Time-Domain Spectroscopy and Density Functional Theory Analysis of Low-Frequency Vibrational Modes of a Benzoxazolium-Coumarin Donor-pi-Acceptor Chromophore
Indian Institute of Science Education and Research Kolkata（印度科学教育研究学院加尔各答分校）；Sri Sathya Sai Institute of Higher Learning（斯里萨蒂亚赛高等学习研究所）；Indian Institute of Technology Gandhinagar（甘地纳加尔印度理工学院）
Magnetic circular dichroism of THz modes and selection rules of Raman-active optical phonons in the polar altermagnet candidate \ce{Mn2Mo3O8}
University of Augsburg（奥格斯堡大学）；Kazan (Volga region) Federal University（喀山（伏尔加沿岸）联邦大学）；Max Planck Institute for Solid State Research（马克斯·普朗克固体研究所）；Budapest University of Technology and Economics（布达佩斯技术与经济大学）；HUN-REN Wigner Research Centre for Physics（匈牙利研究与教育网络维格纳物理研究中心）
