Journal
JOURNAL OF PHYSICS-CONDENSED MATTER
Volume 27, Issue 37, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0953-8984/27/37/375402
Keywords
hydrostatic pressure; vibrational properties; organic crystals; tetracene; Raman spectra; infrared spectra; phonons
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Funding
- EPSRC [EP/F038356/1]
- University of Bahrain
- EPSRC [EP/F038356/1, EP/F036809/1, EP/K013750/2, EP/K013750/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/K013750/1, EP/F038356/1, EP/F036809/1, EP/K013750/2] Funding Source: researchfish
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We present a comprehensive study of the hydrostatic pressure dependence of the vibrational properties of tetracene using periodic density-functional theory (DFT) within the local density approximation (LDA). Despite the lack of van der Waals dispersion forces in LDA we find good agreement with experiment and are able to assess the suitability of this approach for simulating conjugated organic molecular crystals. Starting from the reported x-ray structure at ambient pressure and low temperature, optimized structures at ambient pressure and under 280 MPa hydrostatic pressure were obtained and the vibrational properties calculated by the linear response method. We report the complete phonon dispersion relation for tetracene crystal and the Raman and infrared spectra at the centre of the Brillouin zone. The intermolecular modes with low frequencies exhibit high sensitivity to pressure and we report mode-specific Gruneisen parameters as well as an overall Gruneisen parameter gamma = 2.8. Our results suggest that the experimentally reported improvement of the photocurrent under pressure may be ascribed to an increase in intermolecular interactions as also the dielectric tensor.
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