Lattice dynamics of FeTe: a combined DFT and inelastic neutron scattering study

For all pnictide families DFT calculations of lattice dynamical properties predict a high sensitivity on structural and magnetic degrees of freedom. Comparison with experiment thus can provide valuable information about the appropriate theoretical model. For the 1111 and 122 families, however, DFT significantly overestimates the size of the ordered magnetic moment which potentially hampers such a comparison. In contrast, the Fe chalcogenide family represents a much better test case, as both theory and experiment agree on the existence of large ordered moments. Here we present results of a combined DFT and inelastic neutron scattering study of the phonon dispersion of FeTe. Large parts of the dispersion curves were mapped out at low temperature and compared with DFT results for nonmagnetic and antiferromagnetic phases using various lattice structures. A satisfactory description of the data is obtained only when the Fe-Te distance of the magnetic calculation is used. The spin-polarization itself, however, is found to be of minor importance.