Molecular dynamics simulation of infrared spectra and average structure of benzoic acid crystal

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Abstract
The I.R. spectra of benzoic acid crystal composed of the A configuration were simulated using the method of molecular dynamics, where all degrees of freedom of vibration, rotation and translation were taken into account and the equilibrium charge and charge fluxes were employed in the formulation. The observed spectra were reproduced satisfactorily, and the crystal field effect considered in the simulation led to reasonable shifts of respective frequencies from those calculated by the normal coordinate analysis for an isolated dimer. The most remarkable shifts were observed in the OH stretching (ca. 200 cm−1) and the OH out-of-plane bending (61 cm−1) modes. Far infrared spectra were also obtained in the simulation. The compression of the O … O distance due to the crystal field effect was found to be between 0·04 and 0·05 Å which agreed well with the experimental result.