Elastic, Electronic, and Optical Properties of Two-Dimensional Graphyne Sheet

The elastic, electronic, and optical properties of the 2D graphyne sheet, which consists of hexagonal carbon rings and acetylenic linkages, are investigated from first-principles calculations. Graphyne has a Poisson's ratio of 0.417 and an in-plane stiffness of 10.36 eV/angstrom(2). Compared with graphene, graphyne is much softer because of its relatively smaller number of bonds. The band structure of graphyne is calculated using both generalized gradient approximation and hybrid functional, and the band gap predicted by the latter is twice as much as that given by the former. It is also shown that the energy bands of graphyne can be divided into several regions according to bonding character. The optical property of graphyne is found to be strongly anisotropic. For electric field parallel to the graphyne plane, strong optical adsorption is observed in low-energy region, whereas for the electric field perpendicular to the graphyne plane, the adsorption in the low-energy region is very weak. What's more, the response of the band gap of graphyne to uniform strain is also studied, and we show that the band gap can be continuously modified under the strain.