These effects can also shed light on the 'intramolecular' versus 'intermolecular' hypotheses regarding the origins of the JGβ relaxation . For example, the well-studied glass former, ortho-terphenyl (OTP), is regularly referred to as being 'rigid' in the literature, and has been used as a benchmark in the debate surrounding the origins of the JG-β relaxation. A simple simulation of the gas-phase vibrational properties (using DFT in CP2K) of a single-molecule of OTP puts this description in dispute, however, since there exist a number of lower-frequency features in the vibrational spectrum (< 400 cm -1 ) that are torsional type motions of the OTP ring moieties. These motions will be thermally excited at ambient conditions (using the Boltzmann relation for a 400 cm -1 transition yields an excited state population of ≈ 13% at 298 K), and will contribute to the overall spectral response of OTP. We propose that, rather than restrict a description of the type of motions involved in the various relaxation processes to being either internal or external, it is better to simply refer to the nature of the PES and the energies of the various dynamical variables.