Materials. with perovskite structures have been extensively studied due to their remarkable properties, which are important in various aspects of daily life. In the present approach, Na₂MgSiZ₆ (Z = I, Br, Cl) halides were extensively studied, and it was realized from the band structure results that all these halides display semiconducting natures with indirect band gaps. The semiconducting natures of Na₂MgSiZ₆ (Z = I, Br, Cl) halides were further confirmed by their TDOS results. The optimized values of the lattice constants were found to be 11.70 Å, 10.4 Å, and 10.22 Å for Na₂MgSiI₆, Na₂MgSiBr₆, and Na₂MgSiCl₆, respectively. Moreover, the largest volume was observed for the Na₂MgSiI₆ compound, while the smallest volume was recorded for the Na₂MgSiCl₆ compound. Na₂MgSiCl₆ compound exhibited brittle nature, whereas Na₂MgSiBr₆ and Na₂MgSiI₆ were found to be ductile. All three materials demonstrated attractive values of optical conductivities, making them befitting candidates for solar cells, LEDs, detectors, and various other optoelectronic devices. From the achieved negative values of formation energy for all the Na₂MgSiZ₆ (Z = I, Br, Cl) halides, it was comprehended that these compounds could be synthesized practically.

This study focuses on potassium based double perovskite materials, specifically a series of K₂MgSnZ₆ (Z = Cl, Br, & I) halide materials. For the investigated materials, all primary calculations were performed using the Full-Potential Linearized Augmented Plane-Wave (FP-LAPW) method, supported by density functional theory (DFT), and implemented in the WIEN2k code. The Gold-Schmidt tolerance factor values confirm the structural stability of the compounds, while the negative values of formation energy indicate the feasibility of experimental synthesis of the studied materials. The lattice constants were observed to increase as the halide element at the ‘Z’ position was replaced by one with a larger ionic radius. The recorded band-gap values were 2.60 eV, 2.00 eV, and 1.37 eV for K₂MgSnCl₆, K₂MgSnBr₆, and K₂MgSnI₆, respectively. After calculating the elastic constants for all K₂MgSnZ₆ (Z = Cl, Br, & I) materials, it was found that they satisfy the primary conditions for Born stability required for cubic-phase materials: (1) C₁₁ > B > C₁₂, (2) C₁₁ + 2C₁₂ > 0, (3) C₁₁ > 0, (4) C₄₄ > 0, and (5) C₁₁–C₁₂ > 0. The optical parameters of the K₂MgSnZ₆ (Z = Cl, Br, & I) double perovskite materials suggest that these materials could play a significant role in practical applications such as solar cells, UV detectors, and various optoelectronic devices.