REVERSE MONTE-CARLO SIMULATION OF A HETERONUCLEAR MOLECULAR LIQUID - STRUCTURAL STUDY OF ACETONITRILE

The liquid structure of acetonitrile (AN) has been studied by the rece ntly developed reverse Monte Carlo (RMC) simulation technique. This is the first attempt to apply the method to a heteroatomic molecular liq uid. The basic simulation box contained 512 AN molecules. Each molecul e was represented by three atomic sites, which were held together by ' 'coordination constraints'' allowing a realistic flexibility of the mo lecule. The generated configurations have been refined against experim ental X-ray diffraction data. A Metropolis Monte Carlo simulation was also carried out and proved the reliability of the results of RMC. Par tial pair correlation functions and angular and spatial distributions of the neighbors around a central molecule were calculated and analyze d in terms of predominant orientational configurations. A strong prefe rence for antiparallel and a slight preference for parallel, head-to-t ail, T- or L-shaped configurations were found, in qualitative accordan ce with previous results. These preferences however, decay rapidly aft er the first two to three neighbors. The average coordination number o f the first shell resulted in five to six neighbors; moreover, differe nt ''orientational states'' could be distinguished within the first co ordination shell of molecules.