Spin state of iron—the control parameter of iron-containing HTSC: Dependence of ground state energy, phonon energies and atom positions on the spin state of iron ion in FeTe

Abstract

The density functional theory was applied to calculate the electronic structure, ground state energy, phonon frequencies at the center and at the boundary of the Brillouin zone, as well as the distribution of magnetic moment over d-orbitals of iron in the magnetically ordered phase of FeTe as functions of the magnetic moment—spin state of iron. It was shown that the ground state energy minimum is achieved at a certain distribution of the magnetic moment over d-orbitals and at a certain spin state of the iron ion. The impact of the new type of interaction (“the spin state–lattice” interaction) on the phonon subsystem was studied numerically. It was found that the high-frequency part of the phonon spectra undergoes the most significant changes upon changing the spin state. To describe the properties of iron-containing HTSC compounds, an integral parameter (spin state of iron ion) was suggested.