MOLECULAR-DYNAMICS STUDY OF LOCAL-STRUCTURE AND REORIENTATIONAL DYNAMICS IN LIQUID ACETONITRILE

Local structure and reorientational dynamics in liquid acetonitrile, which are related to intensities and band shapes of the far-infrared spectra, were studied by molecular dynamics calculations. The calculations were performed at 233, 291 and 350 K with two types of potential, with and without Coulomb terms involving fractional charges on each atom in addition to the atom-atom Lennard-Jones terms. Comparison of results of the two types of calculations, MD(LJ + FC) and MD(LJ), shows that the dipole-dipole interaction plays an important role in determining the average local structure and the intermolecular cross-correlation of the reorientational motion. The result of MD(LJ + FC) reproduces well both a relative enlargement of the molecular dipole moment in the liquid phase and a characteristic feature of the rotational velocity correlation function.