DFT plus U based characterization of structural, magnetic, dynamic, elastic and thermodynamic properties of KXF3 (X = Fe or Co) halide perovskites compounds

Density functional theory with the Hubbard corrective coefficient for the cobalt (Co) and iron (Fe) atoms was adopted to calculate the structural, dynamic, and magnetic properties of the KCoF 3 and KFeF 3 perovskites. The Hubbard coefficients for Fe and Co atoms were calculated using the Madsen method and their value are 3.456 eV and 4.025 eV, respectively.The structural stability of these compounds was verified by calculating their negative enthalpies of formation at the most stable state and under the influence of pressure up to 30 GPa. Their dynamic stability was confirmed via the calculation of the phonon dispersions along the high symmetry lines in the first Brillouin region. The temperature dependence of the thermal expansion coefficient, isochoric heat capacity, entropy, and lattice thermal conductivity were calculated for various fixed pressures of 0, 10, 20 and 30 GPa. Temperature dependence of the single crystal and polycristalline elastic moduli were predicted for a temperature range of 0 - 1000 K.