Investigation of hydrogen bonds properties in the terephthalic acid crystal, using molecular dynamics method

• The acid and its deuterated forms were studied by Car–Parrinello molecular dynamics.
• The power and theoretical infrared spectra were calculated for the different systems.
• The theoretical infrared spectra were compared with the experimental data.

The aim of this study was to perform calculations using the method of Car–Parrinello molecular dynamics, leading to the optimized geometry of the molecules of 1,4-benzenedicarboxylic acid (terephthalic acid) in crystals, for the hydrogen form and three variants of substitution of deuterium atoms inside a carboxyl group. Based on the results, trajectories and dipole moments were calculated, what makes possible to simulate vibrations in different systems, and to make calculation of theoretical infrared spectra and atomic power spectra. Theoretical results were compared with the experimental spectra, which verifies the correctness of the method and also was compared with the results obtained by quantum-mechanical calculations using DFT for the isolated dimer. Comparison of the spectra of different forms, allowed for in-depth analysis of the effect of isotopic substitution on the frequency of vibrations and shapes of bands, and confirm the presence of possible coupling effects and intra- and intermolecular interactions. Comparison with the DFT results for the dimer show influence of the crystal structure on the spectra.

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