Electronic structure and optical properties of boron-sulfur symmetric codoping in 4 × 4 graphene systemsChen Huang, Lihong Han, Liyuan Wu, Rui Su, Jun Chen and Pengfei LuEur. Phys. J. B, 88 6 (2015) 147DOI: https://doi.org/10.1140/epjb/e2015-60064-y