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\bibitem{Ullah_etal2015} {\textquotedblleft}\textit{Band-gap tuning of graphene by Be doping and Be, B co-doping : a DFT study}{\textquotedblright}. Ullah S, Hussain A, Syed WA, Saqlain MA, Ahmad I, Leenaerts O, Karim A, RSC advances \textbf{5}, 55762 (2015).   http://doi.org/10.1039/c5ra08061d

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