Ab initio quantum chemical and molecular dynamics simulation study of lithium iodide in acetonitrile

Ab initio calculations for clusters containing Li+ and up to six acetonitrile molecules have been performed by using the B3LYP, MP2(FC) and MP2(Full) methods with the 6-311+G** basis set. The three computational methods give similar results for highly symmetric structures. In the case of MP2 calculation the inclusion of core electrons does not effect the values of the intermolecular distances and binding energy in the Li+-acetonitrile complex. The average ion-ligand distance increases with increasing number of acetonitrile molecules in the cluster. It has been shown that the energy required to incorporate an additional acetonitrile molecule in the Li-acetonitrile clusters containing 5 and 6 acetonitrile molecules is almost equal to the acetonitrile-acetonitrile interaction energy in the most stable acetonitrile dimer and therefore it is very difficult to predict whether the coordination sphere of Li+ contains four, five or six acetonitrile molecules. A molecular dynamics simulation has also been performed on LiI-acetonitrile system. The coordination number of the Li+ and I- have been found to be 5.97 and 14, respectively. The first solvation shell of Li+ has an octahedral geometry; the coordination sphere of the I- ion does not show any special arrangement.