Collective low-frequency excitations in a molecular glass

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Abstract
The collective dynamics of an organic molecular glass former has been investigated by means of coherent inelastic scattering of neutrons at several temperatures below the glass transition. The excitations observed by means of the inelastic neutron scattering response are characterized by the wavevector dependences of their average frequencies. The inelastic spectra are analysed on the basis of a lattice dynamics calculation for the polycrystalline reference state as well as a molecular dynamics simulation of a computer-generated glass. The excitation frequencies are discussed in terms of average omega m quantities, defined as the peak maxima of the longitudinal current-current autocorrelation function. An assessment of the reliability of the simulation results is finally made by comparison with the experimentally accessible magnitudes.