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

• All compounds exhibit a direct bandgap when using GGA+U with spin–orbit coupling. • Europium ions control the magnetic properties of the perovskites. • The compounds absorb primarily in the UV region, with 20% reflectance in the IR and visible regions. • CsEuCl 3 demonstrates a high figure of merit (ZT) about to 1. • The perovskites show promising potential for optical and thermoelectric applications. 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 CsEuX 3 (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 CsEuBr 3 and CsEuI 3 exhibit identical characteristics, whereas CsEuCl 3 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, CsEuCl 3 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.