Electronic structure and optical properties of boron-sulfur symmetric codoping in 4 × 4 graphene systems Chen Huang, Lihong Han, Liyuan Wu, Rui Su, Jun Chen and Pengfei Lu Eur. Phys. J. B, 88 6 (2015) 147 Published online: 08 June 2015 DOI: 10.1140/epjb/e2015-60064-y