On the Ab Initio DFT + U Calculations of the Physical Properties of a Compound with Strong Electron–Electron Correlations by the Case of KFeS₂

The magnetic and electronic properties of quasi-one-dimensional iron chalcogenide compound KFeS₂ have been calculated within two DFT + U approaches based on the simplified LSDA + U approach and rotationally invariant LSDA + U approach. It is shown that the simplified LSDA + U approach with the single parameter ${{U}_{{{\text{eff}}}}}$ correctly describes the magnetic ground state but erroneously predicts the electronic properties. On the other hand, the rotationally invariant LSDA + U approach with two independent parameters U and J provides the correct description of electronic and magnetic properties of KFeS₂ at once. By the comparison of ab initio results with experimental data on magnetic ground state and electronic properties, the values of the parameters U and J have been proposed for the correct description of physical properties of KFeS₂ within the DFT + U approach.