  The gap generation is studied in suspended clean graphene in the continuum
model for quasiparticles with the Coulomb interaction. We solve the gap
equation with the dynamical polarization function and show that, comparing to
the case of the static polarization function, the critical coupling constant
lowers to the value \alpha_c=0.92, which is close to that obtained in lattice
Monte Carlo simulations. It is argued that additional short-range four-fermion
interactions should be included in the continuum model to account for the
lattice simulation results. We obtain the critical line in the plane of
electromagnetic and four-fermion coupling constants and find a second order
phase transition separating zero gap and gapped phases with critical exponents
close to those found in lattice calculations.
