Application of Nuclear Inelastic Scattering Spectroscopy to the Frequency Scale Calibration of Ab Initio Calculated Phonon Density of States of Quasi-One-Dimensional Ternary Iron Chalcogenide RbFeSe2

This study aims to examine the applicability of nuclear inelastic scattering (NIS) and conventional Mossbauer spectroscopy for calibration of the frequency scale of ab initio calculated phonon density of states (PDOS) of iron ternary chalcogenides. NIS measurements are carried out on the quasi-one-dimensional ternary chalcogenide RbFeSe2 to obtain the partial PDOS of the iron atoms in the compound. We compare the experimental PDOS with our previous results on vibrational properties of RbFeSe2 obtained with density functional theory (DFT) ab initio calculations, conventional Mossbauer, and infra-red spectroscopies. The experimental PDOS measured by NIS is collated with the ab initio calculated one. The frequency correction factor for the ab initio results is determined as 1.077, in good agreement with value of 1.08 obtained previously from the temperature dependence of the Lamb-Mossbauer factor of the iron atoms in RbFeSe2. We conclude that nuclear inelastic scattering and temperature dependence of the Lamb-Mossbauer factor in conventional Mossbauer spectroscopy can be equally applied for evaluation of the frequency correction factor for ab initio calculated phonon density of iron of ternary chalcogenides.