Using classical molecular dynamics simulation and the empirical bond-order Tersoff-Brenner potential for the carbon-carbon interaction the phonon density of states of single-wall carbon nanotubes (SWNT) of various chiralities has been studied as a function of temperature and nanotube diameter. The calculated frequencies of the radial breathing mode (RBM) are in excellent agreement with results of an empirical force constant model and in good agreement with ab initio and tight-binding calculations. This allows us to assign low-frequency resonance enhanced Raman modes observed in SWNT bundles.