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See detailHigh-Throughput Investigation of the Geometry and Electronic Structures of Gas-Phase and Crystalline Polycyclic Aromatic Hydrocarbons
Schatschneider, Bohdan; Monaco, Stephen; Liang, Jian-Jie et al

in Journal of Physical Chemistry. C, Nanomaterials and interfaces (2014), 118(34), 19964-19974

The quest for cheap, light, flexible materials for use in electronics applications has resulted in the exploration of soft organic materials as possible candidates, and several polycyclic aromatic ... [more ▼]

The quest for cheap, light, flexible materials for use in electronics applications has resulted in the exploration of soft organic materials as possible candidates, and several polycyclic aromatic hydrocarbons (PAHs) have been shown to be versatile (semi)conductors. In this investigation, dispersion inclusive density functional theory is used to explore all of the current crystalline PAHs within the Cambridge Structure Database (CSD) from both structural and electronic standpoints. Agreement is achieved between the experimental and calculated crystalline structures, as well as the electronic properties. Specifically, variation between the mass densities, unit cell parameters, and intermolecular close contact fractions were within +5\% +/-2\%, and +/-1 of experiment, respectively. It is found that a simple addition of a similar to 1 eV constant to the DFT-PBE gaps provides good agreement with the experimental optical gaps of both gas phase (within +/-2.6\%) and crystalline (within +/-3.5\%) PAHs. Structural and electronic analysis revealed several correlations/trends where ultimately limits in the band gaps as a function of structure are established. Finally, analysis of the difference between band gaps of the isolated molecules and crystals (Delta E-g(Xtal-Mols)) demonstrates that Delta E-g(Xtal-Mols) can be captured qualitatively by PBE and PBE0 functionals, yet significant quantitative deviations remain between these functionals and experiment. [less ▲]

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See detailUnderstanding the Structure and Electronic Properties of Molecular Crystals Under Pressure: Application of Dispersion Corrected DFT to Oligoacenes
Schatschneider, Bohdan; Monaco, Stephen; Tkatchenko, Alexandre UL et al

in Journal of Physical Chemistry. A (2013), 117(34), 8323-8331

Oligoacenes form a fundamental class of polycyclic aromatic hydrocarbons (PAR) which have been extensively explored for use as organic (semi) conductors in the bulk phase and thin films. For this reason ... [more ▼]

Oligoacenes form a fundamental class of polycyclic aromatic hydrocarbons (PAR) which have been extensively explored for use as organic (semi) conductors in the bulk phase and thin films. For this reason it is important to understand their electronic properties in the condensed phase. In this investigation, we use density functional theory with Tkatchenko-Scheffler dispersion correction to explore several crystalline oligoacenes (naphthalene, anthracene, tetracene, and pentacene) under pressures up to 25 GPa in an effort to uncover unique electronic/optical properties. Excellent agreement with experiment is achieved for the pressure dependence of the crystal structure unit cell parameters, densities, and intermolecular close contacts. The pressure dependence of the band gaps is investigated as well as the pressure induced phase transition of tetracene using both generalized gradient approximated and hybrid functionals. It is concluded that none of the oligoacenes investigated become conducting under elevated pressures assuming that the molecular identity of the system is maintained. [less ▲]

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