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    Ground state determination and band gaps of bilayers of graphenylenes and octafunctionalized-biphenylenes
    (Elsevier, 2019-03-25) Junkermeier, Chad E. ; Paupitz, Ricardo
    Device fabrication often requires materials that are either reliably conducting, reliably semiconducting, or reliably nonconducting. Bilayer graphene (BLG) changes from a superconductor to a semiconductor (Ohta et al., 2006) depending on it’s stacking, but because it is difficult to control its stacking, it is not a reliable material for device fabrication (Bistritzer and MacDonald, 2011) [4]. Using DFTB+ (Aradi et al., 2007), this work demonstrates that bilayers of graphenylene, net-C, and net-W can be reliably used for device fabrication without knowing the details of their stackings. Bilayers of graphenylene and net-C are semiconducting for all sheer displacements, net-W is conducting for all sheer displacements, while that Type II, like BLG, is conducting or semiconducting depending on the sheer displacement. The method used gives bond lengths, unit cell dimensions, and band dispersion of single-layer graphene that are consistent with previously reported values, it correctly predicts that AB stacking is the ground state of BLG and gives an interlayer separation that is consistent with previous studies. The bond lengths and lattice constants of the other carbon allotropes are consistent with previously published values. In order to calculate the band structures of the bilayer systems, DFTB+ was first used to determined the interlayer separations of the 2-D carbon allotropes under shear displacement.
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    N -Carbophenes: two-dimensional covalent organic frameworks derived from linear N -phenylenes
    (IOP Publishing, 2019-10-02) Junkermeier, Chad E. ; Luben, Jay Paul ; Paupitz, Ricardo
    N -Carbophene (carbophene) is a novel class of two-dimensional covalent organic frameworks (2DCOF), based on linear N-phenylenes, that have moderate band gaps and low-mobility bands surrounding the Fermi energy; the simplest of which may have been recently synthesized. Using tight-binding density functional theory, the ground state configurations single layers, bilayers, and bulk systems was determined. This work finds that carbophenes have formation energies per carbon atom similar to that of graphenylene. The similarity of formation energies between graphenylene and carbophene suggests that when trying to synthesize one, the other may also be synthesized. The formation energies could explain why the first reported synthesis of graphenylene also indicated that they may have synthesized 3-carbophene. Results contained in this work suggests that a carbophene was synthesized instead of graphenylene. The projected density of states (PDOS) demonstrates that the anti-aromatic nature of the cyclobutene units plays a direct role in the creation of bands around the Fermi level, making this an exciting material in the theoretical understanding of the nature of aromatic bonds.