Lead-free halide double perovskites have undergone extensive scrutiny for their stability, efficiency and environment-supportive quality in multiple optoelectronic frameworks under varying applied pressure. The CASTEP code was used to optimize and analyze the material's properties using the first principles method. These calculations simulated the electronic properties and employed a plane-wave basis set with pseudo-potentials within the DFT framework. This study explores the effect of applied pressure (0–10 GPa) on the properties of \({M}_{2}NaGa{Cl}_{6} (M=K, Rb)\) , aiming to understand how pressure influence their physical characteristics. Simulation result reveal that structural parameters including lattice parameters, volume, formation energy and bond distance are significantly affected by pressure. Notably, the volume is reduced by up to 22% at 10 GPa. The mechanical properties, evaluated through elastic constants and elastic moduli. Machinability index, Kleinman parameter, and Vickers hardness ensure sensitivity of these compounds at distinct applied pressures. Increased pressure enhances ductility which is certified by the Pugh's and Poisson's ratios. Additionally, both compounds exhibit promising optical behavior, especially for optical coatings—thin layers that control light reflection or transmission and optical reflecting cells, which enhance light redirection in devices, and show improved thermodynamic stability at higher pressures. These findings underscore the remarkable prospect of \({M}_{2}NaGa{Cl}_{6} (M=K, Rb)\) for revolutionary applications in the field of optoelectronic engineering, applicable as electro-catalyst, thermo-electronic devices, energy storage devices, quantum dots, solar water splitting, thermal detector, flexible electronics, and heat removing sink, paving the way for advancements in high-performance interfaces.
