  The coupled exciton-vibrational dynamics of a 3-site FMO model is
investigated using the numerically exact multilayer multiconfiguration
time-dependent Hartree approach. Thereby the vibrational mode specific coupling
to local electronic transitions is adapted from a discretized experimental
spectral density. The solution of the resulting time-dependent Schr\"odinger
equation including three electronic and 450 vibrational degrees of freedom is
analyzed in terms of excitonic populations and coherences. Emphasis is put onto
the role of specific ranges of vibrational frequencies. It is observed that
modes between 160 and 300 cm$^{-1}$ are responsible for the subpicosecond
population and coherence decay. Further, it is found that a mean-field approach
with respect to the vibrational degrees of freedom is not applicable.
