Tunable Electronic and Optical Properties of LiN 1 − x P x Mg Half‐Heusler Phases for Advanced Optoelectronic Applications

The structural, electronic, bonding, and optical properties of LiN 1− x P x Mg ( x = 0, 0.25, 0.5, 0.75, and 1) half‐Heusler alloys were investigated using density functional theory within the GGA and modified Becke–Johnson (mBJ) frameworks. Attention was given to the intermediate compositions ( x = 0.25, 0.5, and 0.75), for which detailed theoretical data are not available in the literature. Structural optimization confirms the stability of all investigated compositions and shows that phosphorus substitution leads to a nonlinear expansion of the lattice together with a gradual reduction in stiffness. Among the studied alloys, the x = 0.5 composition exhibits the lowest equilibrium energy, indicating enhanced energetic stability. Electronic structure calculations reveal a clear composition‐dependent evolution of the band gap, with direct‐gap semiconducting behavior preserved up to x = 0.75 and a transition to an indirect band gap in LiPMg ( x = 1). The mBJ calculations predict tunable band gaps ranging from 3.48 to 1.74 eV, highlighting the strong influence of alloying on the electronic properties. Bonding analyses based on COHP, charge transfer, and electron localization function calculations further show that replacing N with P modifies the bonding environment and promotes changes in electron distribution across the lattice. In addition, all compositions exhibit strong optical activity in the visible and ultraviolet regions, characterized by enhanced absorption, optical conductivity, and inter band transitions. These results demonstrate that phosphorus substitution offers an effective route for tailoring the electronic and optical response of LiN 1− x P x Mg alloys, making them promising candidates for future optoelectronic and photonic applications.