  Solvent-free coarse grained models represent one of the most promising
approaches for molecular simulations of mesoscopically large membranes. In
these models, the size of the simulated membrane is limited by the slow
relaxation time of longest bending mode. Here, we present a Monte Carlo
algorithm with update moves in which all the lipids are displaced
simultaneously. These collective moves result in fast excitation and relaxation
of the long wavelength thermal fluctuations. We apply the method to simulations
of a bilayer membrane of linear size $\sim 50 {\rm nm}$ and show reduction of
the relaxation time by two orders of magnitudes when compared to conventional
Monte Carlo.
