Interatomic force constants from first principles: The case of α-quartz

We describe a method for calculating the interatomic force constants in crystalline insulators, from first principles, with explicit inclusion of the long-ranged anisotropic dipole-dipole interaction. Using this technique, the dynamics of -quartz, a model for tetrahedrally bonded silica, is investigated: we examine the range of interatomic forces, their anisotropy, their longitudinal and transverse character, and the importance of the dipole-dipole contribution. These force constants provide an extensive database for testing semiempirical interatomic potentials used in silica molecular-dynamics simulations.