Energetic stability, atomic and electronic structures of extended γ-graphyne: A density functional study.

The energetic stability, atomic and electronic structures of γ-graphyne and its derivatives (γ-GYs) with extended carbon chains were investigated as a function of chain length by density functional calculations in this work. The studied γ-GYs consist of hexagon carbon rings connected by linear chains with C atoms n = 0-22. We predict that the even-numbered C chains of γ-GYs consist of alternating single and triple C-C bonds (polyyne), energetically more stable than the odd-numbered C chains made of continuous C-C double bonds (polycumulene). The calculated electronic structures indicate that γ-GYs can be either metallic (odd n) or semiconductive (even n) depending on the parity of the number of C chain atoms. The semiconducting γ-GYs are predicted to have ~1.2 eV direct band gaps and 0.1-0.2 effective electron masses independent of the chain length. Thus introducing sp carbon atoms into sp (2)-based graphene provides a novel way to open up band gaps without doping and defects while maintaining small electron masses critical to good transport properties. Graphical Abstract The typical atomic model of graphyne (middle) as well as their band gaps (left) and electron density (right).