High-Resolution THz Spectroscopy and Solid-State Density Functional Theory Calculations of Polycyclic Aromatic Hydrocarbons

Abstract

High-resolution and broadband THz spectra of the crystals of nine polycyclic aromatic hydrocarbons (PAHs) are presented. Five PAHs are comprised of ortho-fused benzene rings and the other four of peri-fused benzene rings. THz mode assignment is performed by using the anthracene and pyrene crystals as examples. The performance of the PBE functional augmented by Grimme’s two dispersion correction terms, D* and D3, respectively, are rigorously evaluated against the experimental criteria of frequency and isotope shift (IS). The D* and D3 terms use empirical and semi-classical approach for correcting the London-type dispersion interactions, respectively. The nature of each THz mode simulated by PBE-D* and that by PBE-D3 is quantitatively compared in terms of the percentage contributions of the intermolecular and the intramolecular vibrations to the vibrational energy. We find that the two methods have equivalent performance in reproducing the frequencies, ISs, and nature of THz modes of both the anthracene and pyrene crystals.