Intermolecular potential for acetonitrile based on ab initio calculations

A potential function describing the interaction between two acetonitrile mo lecules in terms of electrostatic, repulsion, induction and dispersion cont ributions was constructed using ab initio calculations of molecular propert ies and IMPT. The minimum energy structure has C-2h symmetry, with the two molecules antiparallel, their centres of mass separated by 3.5 Angstrom, an d the CH bonds in the symmetry plane oriented towards the nitrogen atom of the other molecule. Molecular dynamics simulations carried out with the new potential (many-body effects are included via the induction term) predict that liquid acetonitrile possesses only short range structure, there being no correlation between the orientations of molecules separated by more than 5.2 Angstrom. The induced dipole moment in the liquid is almost parallel t o the molecular axis, and its magnitude is about 20% of the calculated dipo le moment of the isolated molecule.