Graphene monovacancies: Electronic and mechanical properties from large scale ab initio simulations

In this work we have carried out a complete set of large scale density functional theory simulations to characterize the magnetic and mechanical properties of graphene as a function of the monovacancy concentration. Our simulations on systems with up to a G(30 × 30) cell size where we used several thousand k-point meshes –which make them a challenging computational problem– show a clear tendency to converge the local magnetic moment of monovacancies to 2 μB in the diluted limit. Our results confirm that the vacancies experience a Jahn-Teller distortion leading to a 5–9 asymmetric reconstruction and we find a transition to a more symmetric structure when an external isotropic in-plane strain beyond the 2% is applied. Regarding the mechanical properties, we conclude that, even when the presence of monovacancies does not practically affect the in-plane deformations, they induce a strain field that clearly quenches the out-of-plane vibrations, making the defective sample stiffer than its pristine version for a low concentration of vacancies. The 5–9 structure, responsible of this strain field, has been checked to be also stable at room temperature.