Structure and electronic properties of graphyne polymorphs formed from 4-8 graphene

The structure and electronic characteristics of new polymorphic varieties of graphyne, obtained on the basis of the L_4-8 graphene layer, are investigated by the method of the density functional theory in the generalized gradient approximation. Theoretically, seven types of graphite were built: α-L_4-8-, β1-L_4-8-, β2-L_4-8-, β2-L_4-8-, γ1-L_4-8-, γ2-L_4-8-, and γ3-L_4-8-graphyne. However, as a result of geometric optimization, the structure of two graphyne layers (γ2-L_4-8-, and γ3-L_4-8-graphyne) was transformed into a graphene structure. The sublimation energy of the remaining graphite layers is in the range from 6.63 to 6.79 eV per atom. This energy is lower than the sublimation energy of graphene layers, however, it is in the range of sublimation energies characteristic of carbon materials that are stable under normal conditions. The band gap for the graphyne layers is zero or tending to zero, therefore the properties of the layers must be metallic.