DISPERSION CURVES AND FREQUENCY DISTRIBUTION FUNCTIONS IN DIPOLE COUPLED CRYSTALS
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Date
1973
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Ohio State University
Abstract
The dynamics of internal optic modes in crystals can be treated by a molecular dipole model in which the predominant dynamical interactions are due to the vibrationally induced (point) dipoles of the polyatomic species constituting the basis of the crystal lattice. The dipolar interactions can be summed over the lattice by several well known methods; if a wave-vector-dependent dipole sum is calculated it can be shown that the frequency of an internal optic mode can be calculated at any point in the first Brillouin zone in this molecular dipole formalism. This permits the calculation of dispersion curves for internal optic branches along any desired direction in the Brillouin zone as well as the frequency distribution function associated with a particular internal optic branch. Typical calculations of dispersions curves and frequency distribution function for two crystals, $NaN_{3}$ and $KBrO_{3}$, will be presented. The consequences and limitations implied by the use of the molecular dipole model will also be discussed.
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Author Institution: Department of Chemistry, University of Oklahoma