A first-principles study of the vibrational properties of crystalline tetracene under pressure

Abstract

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 Xray structure at ambient pressure and low temperature, optimised 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 Grüneisen parameters as well as an overall Grüneisen parameter γ=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.2

Ab initiophonon dispersion in crystalline naphthalene using van der Waals density functionals

“…The mean absolute percent deviation from experimental data points is 7.8% for DF-cx, 5.8% for PBE (at the experimental geometry), and 12.3% for LDA. These results are consistent with prior reports that PBE at experimental lattice parameters and LDA with relaxed parameters can yield good agreement for naphthalene (at the zone center) and tetracene (throughout the zone), respectively 59,72 . A major drawback of the PBE functional for naphthalene is that it requires prior knowledge of the experimental lattice parameters.…”

“…To our knowledge, only two ab initio phonon band structures of acene crystals have been reported to date 71,72 . The full phonon dispersion of tetracene has recently been calculated using the local density approximation (LDA), capitalizing on the tendency of LDA to overbind to partially compensate for the lack of vdWcorrections 72 .…”

“…The full phonon dispersion of tetracene has recently been calculated using the local density approximation (LDA), capitalizing on the tendency of LDA to overbind to partially compensate for the lack of vdWcorrections 72 . Band structures of solid naphthalene calculated at different pressures have been presented by Fedorov et al 71 using the DFT-D3 approach 40 but without any detailed comparison with experiment.…”

Analytic derivative couplings and first-principles exciton/phonon coupling constants for an ab initio Frenkel-Davydov exciton model: Theory, implementation, and application to compute triplet exciton mobility parameters for crystalline tetracene

“…This is the approach that we take, and our computed phonon modes are in good agreement with those reported in Ref. 67.…”

“…As noted by Abdulla et al, 67 lack of support for dispersion-corrected functionals for phonon calculations presents a major obstacle for studies of conjugated organic systems. A workaround is to forgo the use of a generalized gradient approximation in favor of LDA, as the latter has a tendency to overestimate binding energies, thereby compensating for the absence of attractive dispersion interactions.…”