Molecular-dynamics study of the lattice-vibration contribution to the frequency-dependent dielectric constant of lithium iodide

A molecular-dynamics simulation has been performed on the crystal lithium iodide, LiI. A rigid-ion potential is used with parameters fit to thermal expansion, isothermal compressibility, lattice energy, and the frequency of the transverse optical mode at the zone center. The current-current correlation function has been calculated at T=200 and 400 K, and from this the absorption and dispersion have been obtained. Anharmonic broadening is observed at the higher temperature. In addition, the mean-square displacements of the two ions are found to be 0.013 and 0.031 A${\mathrm{̊}}^2$ at T=200 and 400 K, respectively. The radial distribution function has also been calculated.