Optimal model of semi-infinite graphene for ab initio calculations of reactions at graphene edges by the example of zigzag edge reconstruction

We investigate how parameters of the model of semi-infinite graphene based on a graphene nanoribbon under periodic boundary conditions affect the accuracy of ab initio calculations of reactions at graphene edges by the example of the first stage of reconstruction of zigzag graphene edges, formation of a pentagon-heptagon pair. It is shown that to converge properly the results, the nanoribbon should consist of at least 6 zigzag rows and periodic images of the pair along the nanoribbon axis should be separated by at least 6 hexagons. The converged reaction energy and activation barrier for formation of an isolated pentagon-heptagon pair are found to be -0.15 eV and 1.61 eV, respectively. It is also revealed that such defects reduce the graphene edge magnetization only locally but ordering of spins at opposite nanoribbon edges switches from the antiparallel (antiferromagnetic) to parallel one (ferromagnetic) upon increasing the defect density.

Automated summary

In this study, we investigate the impact of parameters of a model on the accuracy of ab initio calculations of reactions at graphene edges. Specifically, we focus on the reconstruction of zigzag graphene edges and the formation of a pentagon-heptagon pair. Our results show that the nanoribbon should consist of at least 6 zigzag rows and the pair along the nanoribbon axis should be separated by at least 6 hexagons for proper convergence. Furthermore, we find the reaction energy and activation barrier for the formation of an isolated pentagon-heptagon pair. We also observe that these defects only locally reduce the graphene edge magnetization but affect the ordering of spins at opposite nanoribbon edges.