Local Order in Some Aprotic Dipolar Liquids

Abstract

Analysis of the local order in four aprotic, dipolar liquids (acetonitrile, acetone, N,N- dimethylformamide, and pyridine) has been carried out by computer simulation methods. The effect of the dipole-dipole-as well as of the Lennard-Jones interactions on the pair distribution functions and some orientational characteristics are discussed. A general observation for this group of liquids is that the local order is accompanied by a favorable orientation of the nearest neighbor molecules with dipole vectors anti-parallel to the central one. This orientation decays rapidly and extends to slightly more than to the first neighbor molecules only. Differences in local order due to the differences in shapes and symmetries of the molecules are discussed.

The present study partly employs the recently developed Reverse Monte Carlo method, special features of which in contrast to the traditional simulation methods are also discussed.

Key Words:

• Reverse Monte Carlo simulation
• aprotic liquids
• dipolar liquids
• local order in liquids
• acetonitrile
• acetone
• N,N-dimethylformamide
• pyridine