  In our previous paper (Phys. Rev. B {\bf 89}, 165430 (2014)) we have found
that in graphene, in distinction to the four occupied bands, which can be
described by the simple tight-binding model (TBM) with four atomic orbitals per
atom, the two lowest lying at the $\Gamma$-point unoccupied bands (one of them
of a $\sigma$ type and the other of a $\pi$ type) can not be described by such
model. In the present work we suggest a minimalistic model for these two bands,
based on (nearly) free electrons model (FEM), which correctly describes the
symmetry of these bands, their dispersion law and their localization with
respect to the graphene plane.
