  Low-frequency Raman scattering spectra are presented for gold nanocrystals
with diameters 3.5 and 13 nm. The frequencies of the Raman peaks but also their
number are shown to vary with the nanocrystal size. These results are analyzed
using both the continuous elastic medium approximation and an atomistic
approach. We show that the number of atoms in the nanocrystal determines an
upper limit of the number of observable Raman features. The frequency range in
which the continuous elastic medium approximation is valid is defined by
comparison with the calculations based on the atomistic approach.
