Thermoelasticity in organic semiconductors determined with terahertz spectroscopy and quantum quasi-harmonic simulations

Abstract

<p>The thermomechanical response of organic semiconducting solids – an essential aspect to consider for the design of flexible electronics – was determined using terahertz vibrational spectroscopy and quantum quasiharmonic approximation simulations.</p>

The Necessity of Periodic Boundary Conditions for the Accurate Calculation of Crystalline Terahertz Spectra

“…While terahertz spectroscopy was first applied to gases, 72 by far the most widely adopted application of terahertz spectroscopy is in the condensed phase. [13][14][15]17,28 In this regard, terahertz vibrational spectroscopy can be thought of as an extension of the more common mid-IR vibrational spectroscopy (e.g., FTIR) to lower frequencies. While far-IR spectroscopy had been performed over the course of the 20th century, the advent of terahertz timedomain spectroscopy (THz-TDS) instruments around the turn of the century reduced the barrier to accessing this region of the electromagnetic spectrum, and its popularity grew accordingly.…”

“…This has made terahertz spectroscopy a powerful complement to traditional structural methods (e.g., X-ray diffraction) for the identification of different packing geometries, as observed in crystalline polymorphs, for example. [7][8][9][10] On the other hand, the complex and largeamplitude motions occurring at terahertz frequencies have recently been related to a wide-variety of bulk phenomena, for example phase transformations, 11,12 mechanical responses, 5,13,14 electron-phonon coupling, 15,16 and gas-capture in porous mate-persurface to a level of accuracy that enables a proper determination of the weak forces responsible for terahertz dynamics. Over the past two decades there have been a number of advances that have dramatically improved the description of terahertz dynamics, 29 including the determination of IR intensities in periodic simulations, 30 the incorporation of dispersion forces, 31,32 more advanced basis sets, 33,34 force fields, 35 and density functionals, 36 and so on.…”

“…This has made terahertz spectroscopy a powerful complement to traditional structural methods (e.g., X-ray diffraction) for the identification of different packing geometries, as observed in crystalline polymorphs, for example. [7][8][9][10] On the other hand, the complex and largeamplitude motions occurring at terahertz frequencies have recently been related to a wide-variety of bulk phenomena, for example phase transformations, 11,12 mechanical responses, 5,13,14 electron-phonon coupling, 15,16 and gas-capture in porous mate-rials. 17,18 Unfortunately, the factors that make terahertz spectroscopy a valuable analytical technique simultaneously lead to one of its biggest challenges -the interpretation of experimental results.…”

The Necessity of Periodic Boundary Conditions for the Accurate Calculation of Crystalline Terahertz Spectra

“…This has made terahertz spectroscopy a powerful complement to traditional structural methods (e.g., X-ray diffraction) for the identification of different packing geometries, as observed in crystalline polymorphs, for example. [7][8][9][10] On the other hand, the complex and largeamplitude motions occurring at terahertz frequencies have recently been related to a wide-variety of bulk phenomena, for example phase transformations, 11,12 mechanical responses, 5,13,14 electron-phonon coupling, 15,16 and gas-capture in porous mate-persurface to a level of accuracy that enables a proper determination of the weak forces responsible for terahertz dynamics. Over the past two decades there have been a number of advances that have dramatically improved the description of terahertz dynamics, 29 including the determination of IR intensities in periodic simulations, 30 the incorporation of dispersion forces, 31,32 more advanced basis sets, 33,34 force fields, 35 and density functionals, 36 and so on.…”

“…When this criterion is met, experimental terahertz spectra can be used to validate the simulation, enabling access to many related properties that might be difficult to measure experimentally, for example thermodynamic parameters, 28 or interatomic forces. 14 These conditions lead to a powerful methodology for describing dynamic processes with atomic-level precision.…”