Ab initio studies of structural, vibrational, and electronic properties of durene crystals and molecules

We present an ab initio analysis of durene in its gas phase as well as in its crystalline phase by means of density-functional theory. The structural ground-state parameters are determined for three exchange and correlation functionals and compared with experimental data. The crystalline phase is found to be influenced not only by van der Waals bonds but also by weak intermolecular C-H center dot pi hydrogen bonds. The vibrational frequencies and eigenmodes are calculated within the local-density approximation and a one-to-one comparison between both phases is presented. Supplemented by a group-theoretical analysis, we identify infrared-active as well as Raman-active modes and calculate the corresponding IR spectra. The electronic energy levels of durene molecules, as well as the band structure of durene crystals, are calculated from the Kohn-Sham approach. Special emphasis is put on the origin of the large bandwidths and dispersion anisotropy in durene crystals. Possible consequences for the charge-carrier mobilities are discussed.