Structural, phononic and electronic properties of Ge-doped γ-graphynes: A first-principles study

Three stable Ge-doped γ-graphyne-like structures have been systematically studied by first principles calculations based on density functional theory (DFT). These analogues were derived by substituting carbon atoms alternately with Ge atoms in the hexatomic ring of γ-graphyne family and referred to as GeC-graphyne, GeC-graphdiyne and GeC-graphyne-3. These novel systems were found to have planar structures with Ge atoms staying at hexagons with sp2-hybridization. Their dynamical stabilities were confirmed from calculated phonon dispersion spectrums, and their electronic band structures show direct band gap semiconducting behaviors with the band gaps of 1.186 eV, 0.967 eV and 0.828 eV, respectively, indicating that Ge-doping can effectively increase the band gap of pristine γ-graphyne family materials.