First-principles calculation of lattice dynamics and electron-phonon interaction in high pressure phase of solid iodine

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 ω_L=231 cm^-1 and ω_T=159 cm^-1, respectively, at 45 GPa. The phonon frequencies increase with increasing pressure. For example, we have obtained ω_L=260 cm^-1 and ω_T=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.