Application of Frozen-Phonon Method to Lattice Dynamics in FCC Solid Iodine

First-principles frozen-phonon calculations based on the full-potential linearized augmented-plane-wave method are performed for the X point phonon modes of the high-pressure FCC phase of solid iodine. The longitudinal and the transverse phonon frequencies have been evaluated to be ω_L=231 cm^-1 and ω_T=159 cm^-1, respectively, at 45 GPa. The phonon frequencies increase with increasing pressure, i.e. ω_L=260 cm^-1 and ω_T=179 cm^-1 at 64 GPa. The phonon frequencies in the whole Brillouin zone are calculated by expressing the dynamical matrix as the sum of χ and D_o: the generalized electronic susceptibility χ is evaluated by utilizing the electron-phonon interaction obtained microscopically on the basis of the tight-binding scheme and the short-range force term D_o is determined so as to reproduce the X point phonon frequencies obtained by the frozen-phonon method. Pressure effects on the superconductivity of FCC iodine are discussed by using the obtained results.