The optical phonon spectrum of SmFeAsO

We measured the Raman and the infrared phonon spectrum of SmFeAsO polycrystalline samples. We also performed density functional theory calculations within the pseudopotential approximation to obtain the structural and dynamical lattice properties of both the SmFeAsO and the prototype LaFeAsO compounds. The measured Raman and infrared phonon frequencies are well predicted by the optical phonon frequencies computed at the G point, showing the capability of the employed ab initio methods to describe the dynamical properties of these materials. The present study and the comparison among the phonon frequencies of different oxypnictides can provide a theoretical/experimental background for stimulating further investigations on the role of phonons in the physics of these materials.