Lattice dynamics of cryocrystals at high pressure

Abstract

The lattice dynamics of cryocrystals is investigated from first principles in the framework of the Tolpygo model over a wide range of pressures. The phonon frequencies in rare-gas solids are calculated in terms of models that go beyond the scope of adiabatic approximation. At high pressure the phonon spectrum along the D and S directions is distorted and the longitudinal L-and transverse T 2 -modes soften as a result of the electron-phonon interaction, with the relative contribution decreasing in the sequence Ar, Kr, Xe. The calculated phonon frequencies are in good agreement with the experimental data for argon crystals of a pressure 3.1 GPa.PACS: 63.20.Dj Phonon states and bands, normal modes, and phonon dispersion; 63.20.Kr Phonon-electron and phonon-phonon interactions.