Polarizability of molecular clusters as calculated by a dipole interaction model

Abstract

We have developed and investigated a dipole interaction model for calculating the polarizability of molecular clusters. The model has been parametrized from the frequency-dependent molecular polarizability as obtained from quantum chemical calculations for a series of 184 aliphatic, aromatic, and heterocyclic compounds. A damping of the interatomic interaction at short distances is introduced in such a way as to retain a traceless interaction tensor and a good description of the damping over a wide range of interatomic distances. By adopting atomic polarizabilities in addition to atom-type parameters describing the damping and the frequency dependence, respectively, the model is found to reproduce the molecular frequency-dependent polarizability tensor calculated with ab initio methods. A study of the polarizability of four dimers has been carried out: the hydrogen fluoride, methane, benzene, and urea dimers. We find in general good agreement between the model and the quantum chemical results over a wide range of intermolecular distances. To demonstrate the power of the model, the polarizability has been calculated for a linear chain of urea molecules with up to 300 molecules and one- and two-dimensional clusters of C60 with up to 25 molecules. Substantial intermolecular contributions are found for the polarizability anisotropy, whereas the effects are small for the mean polarizability. For the mean polarizability of C60, we find good agreement between the model and experiments both in the case of an isolated molecule and in a comparison of a planar cluster of 25 C60 molecules with experimental results on thin films.