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A new formula for elastic bending modulus of monolayer graphene is derived analytically from an empirical potential for solid-state carbon-carbon atomic bonds. Two physical origins are identified for the non-vanishing bending modulus of the atomically thin graphene sheet, one due to the bond angle effect and the other resulting from the bond order term associated with the dihedral angles. The analytical prediction compares closely with ab initio energy calculations. Pure bending of graphene monolayers into cylindrical tubes are simulated by a molecular mechanics approach, showing slight nonlinearity and anisotropy in the tangent bending modulus as the bending curvature increases. An intrinsic coupling between bending and in-plane strain is noted for graphene monolayers rolled into carbon nanotubes. PACS numbers: 61.48.De, 62.20.de, 81.05.Uw, 82.45.Mp 1 The unique two-dimensional (2D) lattice structure and physical properties of graphene has drawn tremendous interests recently. In particular, rippling of suspended graphene monolayers has been observed, with mesoscopic amplitude and wavelength 1. Imaging of monolayer graphene sheets on silicon dioxide has also shown structural corrugation 2, 3. Theoretical studies 4-6
Lü et al. (Thu,) studied this question.