  The lattice dynamics of FeSb2 is investigated by the first-principles DFT
calculations and Raman spectroscopy. All Raman and infra-red active phonon
modes are properly assigned. The calculated and measured phonon energies are in
good agreement except for the B3g symmetry mode. We have observed strong mixing
of the Ag symmetry modes, with the intensity exchange in the temperature range
between 210 K and 260 K. The Ag modes repulsion increases by doping FeSb2 with
Co. There are no signatures of the electron-phonon interaction for these modes.
