Molecular dynamics study on the anisotropic Poisson's ratio of the graphene

To investigate the property of anisotropic Poisson's ratio in graphene, we use the molecular dynamics (MD) method to simulate the stretching process. Pristine graphene and graphene with Stone - Wales (SW) defect, 5-8-5 defect and di-vacancy defect are investigated. The results show that the Poisson's ratio always depends on the tensile strain and is sensitive to the tensile angle between the tensile direction and the armchair direction. For perfect graphene, its Poisson's ratio will transform from a positive value to a negative value at a critical strain. In the cases of smaller tensile angles, the corresponding Poisson's ratio and the critical strain are smaller, and even the negative Poisson's ratio is observed. For the defective graphene cases, it is found that a negative Poisson's ratio is more easily observed with higher defect concentrations. The negative Poisson's ratios of the graphene with 5-8-5 type defect and SW defect always arise from the wrinkles induced by these topologic defects. However, the negative Poisson's ratio of graphene with di-vacancy defect is caused by the deformation of graphene lattice structure, which is the same as the pristine graphene. The wrinkles in defective graphene are more likely to cause negative Poisson's ratio of graphene than its lattice structure deformations.