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\bibitem{Singh_etal2014} {\textquotedblleft}\textit{Electronic properties of graphene nano-flakes : energy gap, permanent dipole, termination effect, and Raman spectroscopy}{\textquotedblright}. Singh SK, Neek-Amal M, Peeters FM, The journal of chemical physics \textbf{140}, 074304 (2014).   http://doi.org/10.1063/1.4865414

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