A torsional potential for graphene derived from fitting to DFT results Georgios D. Chatzidakis, George Kalosakas, Zacharias G. Fthenakis and Nektarios N. Lathiotakis Eur. Phys. J. B, 91 1 (2018) 11 Published online: 17 January 2018 DOI: 10.1140/epjb/e2017-80444-5