The role of electrostatics in molecular interactions: Prediction of shapes and electronic properties of weakly bound complexes

Using ab initio self-consistent field molecular orbital methods the validity and potential predictive capabilities of electrostatic methods are explored with specific reference to the determination of the shapes of weakly bound molecular complexes and the changes in electronic properties that occur on the formation of a dimer, cluster or crystal. The Van der Waals dimers (H20)2, C12-HF, C1F-HF and N20- HF are studied from the structural point of view while for water other properties, such as dipole moment, dipole moment derivatives and 170 nuclear quadrupole coupling constant are also investigated. In all cases, except for the dipole moment derivatives, the electrostatic effects are shown to account for the major part of the observed effects. Finally, the results of a purely electrostatic calculation of the vapour to solid shift of the 14N nuclear quadrupole coupling constant in ammonia are discussed.