Lattice dynamics of HgSe:: Neutron scattering measurements and ab initio studies -: art. no. 094305

The phonon dispersion relations of HgSe, which is a cubic polar semiconductor with a zero energy gap, has been investigated by means of the coherent inelastic neutron scattering. The complete set of phonon branches has been determined along the [001], [110], and [111] high-symmetry directions. Using the ab initio local-density approximation with ultrasoft pseudopotentials, we have calculated the Hellmann-Feynman forces for 2x2x2 supercell. Applying the direct method, the phonon dispersion relations and the phonon density of states have been derived. They are in good agreement with the results of the neutron-scattering data. The 1x1x10 elongated supercell has been used to find the LO/TO splitting of the optical phonon branches for two different concentrations of free carriers. Higher free-carriers density diminish the LO/TO splitting.