Anharmonic effects on infrared spectra of GaAs and GaP
  With a study of bulk GaAs and GaP, we report detailed infrared spectra and their temperature dependence from first principles. Fine features and low-temperature trends in the predicted response are confirmed by experiment. The spectra are calculated from the far-infrared through twice the frequency of the zone-center optical phonon. The treatment relies on recent developments in the theories of dielectric polarization and the phonon-phonon interaction. 
Hadley M. Lawler and Eric L. Shirley