An ab initio study to investigate the physical properties of CsEuX3 (X=Cl, Br, and I) using different Exchange-Correlation potentials

Several exchange–correlation potentials within the framework of Density Functional Theory (DFT) were used to study the structural, electronic, magnetic, optical, and thermoelectric properties of cubic perovskites CsEuX₃ (X=Cl, Br, and I). The exchange–correlation potentials used in this study include GGA, mBJ, and GGA+U, both with and without spin–orbit coupling (SOC). The stability of all compounds was confirmed by the obtained values of the cohesive energy, formation energy, and tolerance factor. When GGA+U with SOC is used, all compounds show direct bandgap with no effect of the spin state on the bandgap value. The bandgap varies differently for spin-up and spin-down states under pressure. Europium ions control the magnetic properties. Optical investigations indicate that CsEuBr₃ and CsEuI₃ exhibit identical characteristics, whereas CsEuCl₃ has a similar trend but shifted to higher energy. Absorption mostly takes place in the UV region, whereas there is about 20 % reflectance in the infrared (IR) and visible regions. All compounds have low energy loss and excellent transparency. Our investigation indicates that the present compounds are good thermoelectric materials with a high figure of merit. For example, CsEuCl₃ demonstrates a figure of merit (ZT) ranging from 0.82 to 0.86 for spin-up and around 1 for spin-down over the temperature range 50–800 K. Such encouraging results indicate that all compounds are potential candidates for optical applications and thermoelectric devices.