Structural, mechanical and electronic properties of sodium based fluoroperovskites NaXF3 (X = Mg, Zn) from first-principle calculations

The structural stability, mechanical, electronic and thermodynamic properties of the cubic sodium based fluoro-perovskite NaXF3 (X = Mg, Zn) have been studied using density functional theory (DFT). The generalized gradient approximation of Perdew-Burke and Ernzerhof (GGA-PBE) is used for modeling exchange-correlation effects. In addition, the alternative form of the GGA proposed by Engel and Vosko (GGA-EV) is also used to improve the electronic band structure calculations. The results show that both compounds are stable in the cubic Pm3m structure. From Poisson's ratio, it is inferred that cubic antiperovskite NaXF3 are ductile in nature and that bonding is predominantly of ionic in nature. The electronic band structure calculations and bonding properties show that antiperovskites have an indirect energy band gap (M-Γ) with a dominated ionic character. The thermal effects on thermal expansion coefficient, Debye temperature and Grüneisen parameter were predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The calculations are found to be in good agreement with other results.