Phonon calculations in the DFT framework are very costly, in particular when phonons must be calculated throughout the Brillouin zone of a crystal.
However, a full DFT treatment of the phonons is rarely needed. It is sufficient to set up an empirical model for the interatomic interactions and calculate the phonons from the model, and use DFT calculations to determine the parameters in the model. The basic idea of the Coulomb-Hook model is to use charge-charge Coulomb interactions in addition to Hook's law for next-neighbor interactions. We have extended this approach to included anisotropic Born charges.