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 which becomes a superconductor at T ∼ 1 K. The longitudinal and the transverse phonon frequencies have been evaluated to be ωL=231 cm-1 and ωT=159 cm-1, respectively, at 45 GPa. The phonon frequencies increase with increasing pressure. For example, we have obtained ωL=260 cm-1 and ωT=179 cm-1 at 64 GPa. The electron-phonon interaction is evaluated microscopically on the basis of the tight-binding scheme and then the phonon frequencies are calculated in the whole Brillouin zone by introducing appropriate short-range force constants. The results obtained are discussed in connection with pressure effects on superconductivity of FCC iodine.
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