LOCAL ORDER IN SOME APROTIC DIPOLAR LIQUIDS

Analysis of the local order in four aprotic, dipolar liquids (acetonit rile, acetone, N,N-dimethylformamide, and pyridine) has been carried o ut by computer simulation methods. The effect of the dipole-dipole-as well as of the Lennard-Jones interactions on the pair distribution fun ctions and some orientational characteristics are discussed. A general observation for this group of liquids is that the local order is acco mpanied by a favorable orientation of the nearest neighbor molecules w ith dipole vectors antiparallel to the central one. This orientation d ecays rapidly and extends to slightly more than to the first neighbor molecules only. Differences in local order due to the differences in s hapes and symmetries of the molecules are discussed. The present study partly employs the recently developed Reverse Monte Carlo method, spe cial features of which in contrast to the traditional simulation metho ds are also discussed.