  Both van der Waals corrected density functional theory and classical
calculations show that the potential relief of interaction energy between
layers of graphite and few-layer graphene can be described by a simple
expression containing only the first Fourier components. Thus a set of physical
quantities and phenomena associated with in-plane relative vibration,
translational motion and rotation of graphene layers are interrelated and are
determined by a single parameter characterizing the roughness of the potential
energy relief. This relationship is used to estimate the barriers to relative
motion and rotation of graphene layers based on experimental measurements of
shear mode frequencies.
