Molecular dynamics simulations of fully hydrated Dipalmitoylphosphatidylcholine bilayers,
extending temporal and spatial scales by almost one order of magnitude, are presented.
The present work reaches system sizes of 1024 lipids and times 10-60 ns. The simulations
uncover significant dynamics and fluctuations on scales of several nanoseconds, and
enable direct observation and spectral decomposition of both undulatory and thickness
fluctuation modes. Although the former modes are strongly damped, the latter exhibit
signs of oscillatory behavior. From this, it has been possible to calculate mesoscopic
continuum properties in good agreement with experimental values. A bending modulus
of 4 x 10(-20) J, bilayer area compressibility of 250-300 mN/m, and mode relaxation
times in the nanosecond range are obtained. The theory of undulatory motions is revised
and further extended to cover thickness fluctuations. Finally, it is proposed that
thickness fluctuations is the explanation to the observed system-size dependence of
equilibrium-projected area per lipid.