Density functional study of α-graphyne derivatives: Energetic stability, atomic and electronic structure

• α-Graphynes with various C atoms on hexagon edges were studied by DF calculations.
• Parity dependences exist for stabilities, geometries, and electronic structures.
• α-Graphynes with even Nedge have Dirac cones with 70–80% Ve of graphene.
• α-Graphynes with odd Nedge are metallic.
• Tuning the parity of Nedge leads to metallic or Dirac cone electronic structures.

The energetic stability, atomic and electronic structures of α-graphyne and its derivatives (α-GYs) with extended carbon chains were investigated by density functional (DF) calculations in this work. The studied α-GYs consist of hexagon carbon rings sharing their edges with carbon atoms N=1–10. The structure and energy analyses show that α-GYs with even-numbered carbon chains have alternating single and triple C–C bonds (polyyne), energetically more stable than those with odd-numbered carbon chains possessing continuous double C–C bonds (polycumulene). The calculated electronic structures indicate that α-GYs can be either metallic (odd N) or semiconductive (even N) depending on the parity of number of atoms on hexagon edges despite the edge length. The semiconducting α-graphyne derivatives are found to possess Dirac cones (DC) with small direct band gaps 2–40 meV and large electron velocities 0.554×106–0.671×106 m/s, 70–80% of that of graphene. Our DF studies suggest that introducing sp carbon atoms into the hexagon edges of graphene opens up an avenue to switch between metallic and DC electronic structures via tuning the parity of the number of hexagon edge atoms.

Figure optionsDownload as PowerPoint slide