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

Inelastic neutron scattering (INS) and single crystal diffraction measurements of tetramethylbenzene (durene) are reported along with first-principles calculations, based on density functional theory (DFT), of structure and dynamics. Atomic positions obtained from refinement of the neutron scattering data and from three different DFT methodologies are in excellent agreement. Normal modes and INS spectra are calculated within the harmonic approximation using the direct cell finite displacement technique. DFT affords a reliable description of intramolecular and intermolecular interactions with the result that the vibrational spectra are well reproduced by all calculations. The advantage over traditional ab initio, single molecule calculations is the improved description of the low frequency vibrations that are influenced by intermolecular interactions. No refinement of force constants has been undertaken. This structural and vibrational analysis is discussed in the context of optical work in durene host lattices. (C) 2000 Elsevier Science B.V. All rights reserved.