Elastic and Fracture Properties of Single Walled Pentagraphene Nanotubes

Abstract: Membranes of carbon allotropes comprised solely of densely packed pentagonal rings, known as pentagraphene, 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 pentagraphene membranes, the so-called pentagraphene nanotubes (PGNTs). Single-walled PGNT of three distinct configurations: zigzag, $\alpha$-armchair, and $\beta$-armchair 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 $18-21\%$, and ultimate tensile stress of $85-110 GPa$. We also observed auxetic behavior. During stretching at room temperature, we observed a transition between $\beta$-armchair to $\alpha$-armchair PGNT close to the critical strain. With relation to fracture patterns, we observed that mechanical failure starts at bonds mostly aligned to the stretching direction and after tube radial collapse.