Due to the importance of vibrations in the rapid degradation mechanism of many explosives and propellants, vibrational properties of energetic materials have been studied extensively, mainly by using (PBC-)DFT. In many cases, a blue shift of the spectroscopic signals was observed. However, it must be noted that different vibrational modes react differently to pressure, depending on the precise manner in which the vibrational motions are restricted by the environment, e.g., some vibrational modes in C 60 that include a high proportion of radial motion are red shifted upon compression. In such cases, intermolecular effects are likely the cause of the observed red shift.