Optical vibrations in alkali halide crystals

Abstract

We consider long-wave phonon-polaritons and longitudinal optical phonons in alkali-halide ionic crystals. The model of point charges that are polarized in the self-consistent electromagnetic field in a dielectric environment is used. The standard dispersion laws for both branches of phonon-polaritons and longitudinal optical phonons are obtained. The transversal optical phonon frequency is found from the electrostatic equilibrium condition. It is proved by comparison with tabular data that the found frequency coincides with the ion plasma frequency multiplied on the relation $\sqrt{({\epsilon }_{\infty }+2)/(3({\epsilon }_0-{\epsilon }_{\infty }))},$ where ${\epsilon }_{\infty }$ and ${\epsilon }_0$ are the high-frequency dielectric constant and the static one respectively.

keywords{ Alkali-halide ionic crystal; self-consistent electromagnetic field; long-wave oscillations; phonon-polariton; longitudinal optical phonon; electrostatic equilibrium; dielectric constant.} PACS{Phonons in crystal lattices, 63.20. e, Electrostatic waves and oscillations plasma waves, 52.35.Fp, Collective effects 71.45.-d}

References in corpus (1)

• Ab initio Wannier-function-based correlated calculations of Born effective charges of crystalline Li${}_2$O and LiCl