Volume 114, Number 3, May 2016
|Number of page(s)||6|
|Section||Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties|
|Published online||31 May 2016|
Vibrational signatures in the THz spectrum of 1,3-DNB: A first-principles and experimental study
1 Theoretical Division, Los Alamos National Laboratory - Los Alamos, NM 87545, USA
2 Center for Integrated Nanotechnologies, Los Alamos National Laboratory - Los Alamos, NM 87545, USA
3 Lujan Neutron Scattering Center, Los Alamos National Laboratory - Los Alamos, NM 87545, USA
4 Shock and Detonation Physics, Los Alamos National Laboratory - Los Alamos, NM 87545, USA
Received: 13 January 2016
Accepted: 17 May 2016
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.
PACS: 78.30.-j – Infrared and Raman spectra / 31.70.Ks – Molecular solids / 71.15.Mb – Density functional theory, local density approximation, gradient and other corrections
© EPLA, 2016
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