Ab-initio calculation of electronic structure and optical properties of AB-stacked bilayer α-graphyne

• The optical spectra of the AB-stacked bilayer closely resemble to that of the monolayer.
• The electronic spectrum has two Dirac cones for AA stacked bilayer α-graphyne.
• For AB-stacked bilayer the linear bands changes into parabolic bands.

Monolayer α-graphyne is a new two-dimensional carbon allotrope with many special features. In this work the electronic properties of AA- and AB-stacked bilayers of this material and then the optical properties are studied, using first principle plane wave method. The electronic spectrum has two Dirac cones for AA stacked bilayer α-graphyne. For AB-stacked bilayer, the interlayer interaction changes the linear bands into parabolic bands. The optical spectra of the most stable AB-stacked bilayer closely resemble to that of the monolayer, except for small shifts of peak positions and increasing of their intensity. For AB-stacked bilayer, a pronounced peak has been found at low energies under the perpendicular polarization. This peak can be clearly ascribed to the transitions at the Dirac point as a result of the small degeneracy lift in the band structure.