COLLECTIVE EXCITATIONS IN LIQUID METHANOL - A COMPARISON OF MOLECULAR, LATTICE-DYNAMICS, AND NEUTRON-SCATTERING RESULTS

The collective dynamics of liquid methanol-d4 is studied by means of molecular-dynamics simulation. The model potential is validated by means of lattice energy calculations and shows a very good agreement with the experimentally obtained crystal structure. Center-of-mass density and momentum fluctuations are investigated in the (Q,omega) region which is also accessible to inelastic neutron-scattering (INS) techniques. A simple viscoelastic model previously used for the analysis of INS data is tested against the dynamic structure factor computed from the simulation. A direct comparison with the INS results themselves is also made and qualitative agreement is found. Also, a tentative assignment of the peaks appearing in the current-current correlations is made on the basis of lattice-dynamics calculations for the polycrystalline low-temperature alpha-phase.