Strength and fracture of graphyne and graphdiyne nanotubes

This paper investigates the mechanical behavior of γ-graphyne and γ-graphdiyne nanotubes under tensile loading using Molecular Dynamics (MD). Although the existence of these carbon allotropes have been theoretically proposed, and in some cases experimentally demonstrated, their mechanical behavior is still largely unknown. Their structure presents a challenge for MD forcefields since the coexistence of sp and sp2 hybridized carbons atoms forming simple, aromatic and triple bonds is not an easy modelling task. In this work, the tensile behavior of these nanotubes is studied taking the approach of two different potentials: the well-known AIREBO potential, and ReaxFF. Energy-strain curves and stress-strain curves are obtained for each nanotube according to the different potentials and then mechanical properties are calculated and compared. This study is complemented with bond length variation analysis for selected bonds and analysis of the variation of amplitude in interior angles of aromatic rings. Lastly, fracture mechanisms are proposed based on the quantitative analysis and on the visualization of the initial stage of the nanotube's fracture.