From static to tunable: Strain-engineered functional modulation in Mg3PX3(X = I, Br, Cl, and F) inorganic perovskites using first-principles calculations

• Perovskites M g 3 P X 3 (X=I, Br, Cl, and F) • Biaxial compressive and tensile strain • Mg-cation's impact on physical properties • M g 3 P I 3 , M g 3 P B r 3 , M g 3 P C l 3 have an indirect bandgap of 0.4726 eV, 1.4705 eV, 2.3284 eV. • Band gaps of all structures change with strain. Over several years, solar technology has been concentrating on inorganic perovskite-based materials due to their unique optical, electrical, and structural properties. This study explored the influence of biaxial compressive and tensile strain on the optical, electrical, and structural attributes of the inorganic halide perovskites M g 3 P X 3 (X=I, Br, Cl, and F) in detail, applying first-principles density-functional theory (FP-DFT). The work notably pioneered the identification of the Mg-cation's impact on the optical, electrical, and structural properties of inorganic perovskites. The semiconductor substances M g 3 P I 3 , M g 3 P B r 3 , M g 3 P C l 3 have an indirect bandgap of 0.4726 eV, 1.4705 eV, 2.3284 eV between the points of R and Γ(gamma), and M g 3 P F 3 have a direct bandgap of 3.5028eV at the Γ(gamma)-point, based on the electronic band structures. The bandgaps of the M g 3 P I 3 , M g 3 P B r 3 , M g 3 P C l 3 and M g 3 P F 3 Perovskites have band gaps of 0.6477 eV, 1.8032 eV, 2.6710 eV, and 4.3676 eV, while the spin-orbital coupling (SOC) quantum effect is also gradually taken into account. Similarly, bandgaps of all structures tend to increase with compressive load and decrease under tensile strain. The visible part of the spectrum can be significantly absorbed, exhibited by losses of electron ratios, owing to optical metrics like dielectric functions, absorption parameters, heat capacity, entropy, Elastic constants, Poisson's ratio, anisotropic factor, Pugh's ratio, bulk modulus, and the band characteristics of these materials. Reduced compressive strain leads to a redshift in the dielectric constant, reaching its highest value of M g 3 P X 3 (X=I, Br, Cl, and F), whereas reductions in tensile strain cause a blueshift. The M g 3 P X 3 (X=I, Br, Cl, and F) perovskites are highly suitable for use in energy storage systems and light regulation in solar cells because of their properties. Energy bandgap of the Mg 3 PX 3 (X=I, Br, Cl, and F) varies in response to induced strain, involving SOC and with SOC