(A = K or Ag) fluoro-perovskites compounds*

Born effective charges Z_{(i),β α}^*, dielectric tensors ε_α,β and the dynamic stability for AgMgF₃ and KMgF₃ compounds were treated based on the harmonic and quasi-harmonic theory implemented in phonopy code. The band gap for both compounds, and the effective masses of electrons and holes are calculated at different pressures using the TB-mBJ (GGA) approximation within the framework of the density functional theory. Furthermore, absorption coefficient, refractive index, extinction coefficient, reflectivity, and optical conductivity, for both compounds, were calculated. On the other hand, we studied the nature of atomic bonds by the topological distribution of the charge density as well as computing the effective charge of each atom based on the Quantum Theory of Atoms in Molecules (QTAIM) as implemented in Bader code, therefore the ionic type for bonds was explored. The mechanical stability was verified the elastic behavior at the equilibrium ground-state for both compounds. Thermal properties such as heat capacity at constant volume, entropy, Debye temperature, and thermal expansion coefficient are treated depending on the quasi-harmonic model. They are examined under both pressure and temperature influences. The thermoelectric properties of the compound AgMgF₃ showed a high figure of merit (ZT) reached 0.75 at a temperature of 300 K in the case if it was grafted with a concentration of 10²¹ cm⁻³ of n-type.