A bond charge model for the lattice dynamics of iodine

A lattice dynamical model for crystalline iodine has been investigated. The simple bond charge (SBC) model developed by Parr and co-workers (1968, 69, 71 and 73) for free molecules has been adapted for the iodine molecular crystal to take account of intermolecular as well as intra-molecular covalent bonds. Mode instabilities of previous models are absent from the present calculations. Acceptable agreement with experimental dispersion relations has been achieved using model parameters consistent with the basic concepts of the SBC model. The results strongly support the validity of the SBC model for the covalent bonds between halogen atoms.