VIBRATIONAL MODES AND IR-ABSORPTION OF SOME ACENE-BASED MOLECULAR JUNCTIONS. A DFT APPROACH AS IMPLEMENTED IN FHI-AIMS CODE

Abstract

There has been a recent surge in interest in studying molecular junctions made up of small acenes, such as anthracene, tetracene, and pentacene. Apart from the known transport properties exhibited by molecular junctions, there are other areas of interest, such as photothermal applications. Materials that can absorb and convert infrared radiation into heat energy can be applied in these areas. Density functional theory (DFT) calculations were used to evaluate the IR absorption of some acene-based MJs, as well as their rotational and translational energies. The results obtained were then compared with previously reported work on acene molecules. It is found that the total energy and maximum forces of these MJs converged, and the structures relaxed to the minimum possible energy. For the vibrational analysis, the maximum IR-absorption of 4.92 D²/Ų was observed at a frequency of 688.52 cm^-1 for an anthracene MJ. It is 2.17 Debye square per Armstrong square (D2/Å2) at a frequency of 3411.82 cm-1 and 2.93 D2/Å2 at a frequency of 648.71 cm-1 for tetracene and pentacene MJs, respectively. IR absorption at different frequencies enables one to choose the desired materials for a specific task at a given frequency.