  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.
