Anisotropic mechanical behavior and auxeticity of penta-graphene: Molecular statics/molecular dynamics studies

We investigate the mechanical properties of penta-graphene (PG), a recently proposed two-dimensional carbon allotrope using atomistic simulation techniques combined with the empirical description of interatomic interactions. We report on the dependence of its three in-plane mechanical moduli (i. e. Young's modulus, Poisson's ratio and shear modulus) on the deformation direction, strain and temperature. We show that PG displays a strongly manifested mechanical anisotropy, being characterized by Poisson's ratio and the shear modulus which both depend strongly on the deformation direction. By analyzing bond energies we study the influence of different carbon-carbon bonds on the mechanical response of PG and based on that we explain the origins of the observed anisotropy. We show that it is mostly a consequence of the characteristics of the sp(3)-hybridizied bonds, which form the diamond-like tetrahedral blocks. We investigate the auxeticity of PG in detail and show that it displays complete auxetic behavior, having negative Poisson's ratio for all the deformation directions. We show that the auxeticity of PG is similar to that of defective graphene containing 5-8-5 double vacancies, as it also originates from the so-called de-wrinkling mechanism. We study the influence of temperature and show that it only slightly affects the mechanical moduli of PG. (c) 2019 Elsevier Ltd. All rights reserved.