MD Calculated Structural Properties of Clusters in Liquid Acetonitrile/Water Mixtures with Various Contents of Acetonitrile

Abstract

The diversity of the water and acetonitrile structures in a binary system, caused by local structural inhomogeneities, has been investigated by molecular dynamic simulations. Our systems cover a broad range of acetonitrile mole fractions: dilute, moderate, and higher concentration mixtures. For reference, we perform simulations on pure water and pure acetonitrile systems. We examine concepts of analysis for an extraction of local structure information of anisotropic fluids. In general, the local water and acetonitrile structures can be roughly characterized by the radial distribution functions in terms of the classical site−site pair correlations. For a more thorough investigation of the local structure and the microheterogeneity of the systems, we use angular-dependent radial distribution functions. From the radial pair correlation functions, it is possible to extract coordination numbers and detailed local information of anisotropic water distributions around the acetonitrile molecules. To confirm the existence of the acetonitrile cluster and to gain qualitative insight into its stability, we examined the time-dependent radial and angular distribution functions. The results for the acetonitrile cluster arrangements are in line with experimental data of binary acetonitrile/water mixtures.