The roles of π electrons in the electronic structures and optical properties of graphyne

The electronic structures and optical properties of graphyne consisting of sp- and sp(2)-hybridized carbon atoms are studied using first-principles calculations. A tight-binding model of the 2p(z) orbitals are proposed to describe the electronic bands near the Fermi level. The results show that the natural band gap of graphyne originates from the inhomogeneous pi bindings between differently-hybridized carbon atoms. The interlayer interactions of bulk graphyne narrow the band gap to 0.16 eV and result in redshift of the optical spectral peaks as compared to single-layered graphyne.