Mechanical properties of single-walled penta-graphene-based nanotubes: A DFT and Classical molecular dynamics study

Membranes of carbon allotropes comprised solely of densely packed pentagonal rings, known as penta-graphene, exhibit negative Poisson's ratio (auxetic behavior) and a bandgap of 3.2 eV. In this work, we investigated the structural stability, mechanical and fracture properties of nanotubes formed by rolling up penta-graphene membranes, the so-called penta-graphene nanotubes (PGNTs). Single-walled PGNT of three distinct configurations: (n, 0), and two types of (n, n) (here called alpha and beta) were studied combining first-principles calculations and reactive molecular dynamics simulations. Our results showed Young's modulus values of 680-800 GPa, critical strain of 18-21%, ultimate tensile stress of 85-110 GPa, and Poisson's ratio values ranging from -0.05 to -0.30 (auxetic behavior). During stretching at room temperature, we observed a transition from beta-(n, n) to alpha-(n, n) PGNT near the critical strain. Fracture of PGNTs starts at the bonds that are mostly aligned to the stretching direction and after nanotube radial collapse.