  We perform molecular-dynamics simulations of the vibrational and the
elasto-plastic properties of polymeric glasses and crystals and corresponding
atomic systems. We evidence that the elastic scaling of the density of states
in the low-frequency boson peak (BP) region is different in crystals and
glasses. Also, we see that the BP of the polymeric glass is nearly coincident
with the one of the atomic glasses, thus revealing that the former -
differently from elasticity - is controlled by non-bonding interactions only.
Our results suggest that the interpretation of the BP in terms of macroscopic
elasticity, discussed in highly connected systems, does not hold for systems
with low connectivity.
