Ab initio calculations of phonon dispersion in CdGa$_{2}$Se$_{4}$

The density of phonon states and the phonon dispersion in the Brillouin zone are calculated by the density functional method of. The displacements of atoms in the elementary cell are constructed for vibrations of the $A$, $B$, and $E$ symmetries. The calculated frequencies of optical phonons are consistent with the experimentally determined frequencies from the IR-absorption (infrared) and Raman-scattering spectra. In the $xy$ plane, the intersection of low-frequency optical phonons with acoustic phonons is observed.