There are many two-dimensional (2D) structures of carbon allotropes which have been at the center of theoretical and experimental studies in recent years. α-, α2-, β- and γ-graphyne as the graphene allotropes with mixed sp1 and sp3 bonds are under study in the present work utilizing the molecular dynamics (MD) simulations. These thermodynamically stable forms of 2D carbon structure can also be rolled-up to generate novel nanotubes (NTs). Hence, the armchair (-A) and zigzag (-Z) NTs of the aforementioned one-atom-thick planar structures and their buckling behavior (critical force and strain) are considered. It is observed that γ-A- and γ-Z-graphyne NTs have the highest critical forces through the chosen range of aspect ratios (length/radius), whereas the α-graphyne NTs have the lowest critical forces. Also, α2- and β-graphyne NTs have the highest and lowest critical strains, respectively. Furthermore, the possible multi-walled (MW) NTs are simulated. In agreement with results of the single-walled (SW) NTs, the buckling analysis of MWNTs shows that γ-graphyne and α-graphyne MWNTs have the highest and the lowest mechanical stability under compression, correspondingly. In addition, the results of the critical strain for MWNTs are comparable with those of SWNTs.
