A general purpose acetonitrile interaction potential to describe its liquid, solid and gas phases

A flexible and polarizable force field to describe acetonitrile in its three states of matter has been developed on the basis of an ab initio potential energy surface at the MP2 level. The acetonitrile molecule is represented by a sophisticated twelve-site model: the six nuclei plus six mobile charges. Three thousands structures have been employed for the fitting including monomers, dimers and trimers. Gas phase behavior has been tested by analyzing aggregates from dimers to 27-mer which give accurate reproducibility of the experimental and quantum-mechanical results. Classical MD simulations have been performed for the liquid and its crystalline α- and β-forms. An analysis of liquid in a wide range of structural, dynamic, energetics and spectroscopic properties has been performed, as well as neutron diffraction data. Comparison with experimental information is satisfactory. Due to the first principles nature and the polarizable character of this force field properties of the three states of matter are properly reproduced.