▎ 摘　　要

We show that the key formula in the works of Ding et al. [K.-H. Ding, Z.-G. Zhu, and J. Berakdar, Phys. Rev. B 79, 045405 (2009); 84, 115433 (2011); K.-H. Ding, Z.-G. Zhu, Z.-H. Zhang, and J. Berakdar, Phys. Rev. B 82, 155143 (2010)] is invalid in the extended graphene system they investigated. The correct formalism in the extended infinite system is also presented in this Comment.