Classical molecular dynamics simulations have been performed to investigate five mechanical properties of defective penta-graphene under uniaxial tension, namely Young's modulus, Poisson's ratio, ultimate tensile stress, ultimate strain, and toughness. The reliable Erhart-Albe formulation of the Tersoff potential has been used in the simulations and monovacancies are the only kind of structural defect studied. The effects of defect density, chirality, and temperature on the mechanical properties are reported and thoroughly discussed. The results show that by incorporating defects up to 20%, Young's modulus is decreased by more than one order of magnitude and the sign of the mean Poisson's ratio changes to positive, which indicates the possibility of tuning this ratio. Furthermore, the anisotropic behavior of the material is not strong in terms of Young's modulus, ultimate stress, and ultimate strain and at higher temperatures, the ultimate stress, ultimate strain, and toughness almost converge for pristine and defective penta-graphene. It can be concluded that PG is an auxetic material while it can be tuned by defect engineering to behave as classic material. It should be noted that the results of current study can be used as benchmark for design and fabrication of novel potential industrial materials with both negative and positive Poisson's ratios.
