  Acoustic vibrations of nanoparticles made of materials with anisotropic
elasticity and nanoparticles with non-spherical shapes are theoretically
investigated using a homogeneous continuum model. Cubic, hexagonal and
tetragonal symmetries of the elasticity are discussed, as are spheroidal,
cuboctahedral and truncated cuboctahedral shapes. Tools are described to
classify the different vibrations and for example help identify the modes
having a significant low-frequency Raman scattering cross-section. Continuous
evolutions of the modes starting from those of an isotropic sphere coupled with
the determination of the irreducible representation of the branches permit some
qualitative statements to be made about the nature of various modes. For
spherical nanoparticles, a more accurate picture is obtained through
projections onto the vibrations of an isotropic sphere.
