A molecular dynamics-based method is used to compute the vibrational spectra and dispersion curves of a polyethylene chain. The results are compared and contrasted with those of normal mode calculations, demonstrating the validity of the approach and providing fundamental insight into a number of dynamical processes. The strength of the method is its computational efficiency and that it represents an exact classical dynamics approach to calculating vibrational spectra, thereby eliminating many of the weaknesses of normal mode calculations (i.e., the harmonic approximation).