Vibrational properties and lattice specific heat of RbFeS2

In the present work, we have performed an ab initio calculation of vibrational properties of antiferromagnetic ternary iron sulfide KFeS2 utilizing density functional theory. Element specific and total phonon densities of states (PDOS) were calculated within direct approach of harmonic approximation. We used phonon density of states to calculate lattice contribution to the specific heat. The calculated phonon density of states shows a large number of high-frequency vibrational modes of Fe and S atoms, which strongly restricts application of the Debye model for analysis of the thermodynamical properties of quasi-one-dimensional compound KFeS2. The results of the present paper could be used in further analysis of thermodynamical, optical and magnetic properties of KFeS2 compound.