The structure and dynamics of crystalline durene by neutron scattering andnumerical modelling using density functional methods

Inelastic neutron scattering (INS) and single crystal diffraction measureme nts of tetramethylbenzene (durene) are reported along with first-principles calculations, based on density functional theory (DFT), of structure and d ynamics. Atomic positions obtained from refinement of the neutron scatterin g data and from three different DFT methodologies are in excellent agreemen t. Normal modes and INS spectra are calculated within the harmonic approxim ation using the direct cell finite displacement technique. DFT affords a re liable description of intramolecular and intermolecular interactions with t he result that the vibrational spectra are well reproduced by all calculati ons. The advantage over traditional ab initio, single molecule calculations is the improved description of the low frequency vibrations that are influ enced by intermolecular interactions. No refinement of force constants has been undertaken. This structural and vibrational analysis is discussed in t he context of optical work in durene host lattices. (C) 2000 Elsevier Scien ce B.V. All rights reserved.