  The vibrational density of states of silicon nanoparticles in the range from
2.3 to 10.3 nm is studied with the help of molecular-dynamics simulations. From
these simulations the vibrational density of states and frequencies of
bulk-like vibrational modes at high-symmetry points of the Brillouin-zone have
been derived. The results show an increase of the density of states at low
frequencies and a transfer of modes from the high-frequency end of the spectrum
to the intermediate range. At the same time the peak of transverse optical
modes is shifted to higher frequencies. These observations are in line with
previous simulation studies of metallic nanoparticles and they provide an
explanation for a previously observed discrepancy between experimental and
theoretical data [C. Meier et al., Physica E, 32, 155 (2006)].
