DFT insights into bandgap engineering of lead-free LiMCl3 (M = Mg, Be) halide perovskites for optoelectronic device applications

In this theoretical analysis, the pressure-dependent structural, electronic, mechanical, and optoelectronic properties of LiMCl₃ (M = Mg, Be) have been calculated using density functional theory within the framework of the GGA PBE and hybrid HSE06 functional. At ambient pressure, the calculated lattice parameters of LiMCl₃ match well with previously reported values, validating the accuracy of this study. Geometry optimization reveals that under increasing hydrostatic pressure, both the lattice parameters and the unit cell volume decrease. Additionally, the band structure exhibits notable phenomena over the pressure range from 0 to 100 GPa. For the LiMgCl₃ compound, the bandgap decreases from an indirect bandgap of 4 eV to a direct bandgap of 2.563 eV. Similarly, LiBeCl₃ shows an indirect bandgap that decreases from 2.388 eV to 0.096 eV over the pressure range from 0 to 100 GPa. The optical properties of LiMCl₃, including absorption coefficient, reflectivity, refractive index, dielectric function, and conductivity, have been calculated throughout the study under varying pressure conditions. The analysis reveals that the optical properties of LiMCl₃ (M = Be, Mg) enhance with increasing hydrostatic pressure, thereby rendering these materials more suitable for optoelectronic applications. To assess the stability of these compounds, elastic constants were analyzed, indicating that LiMCl₃ exhibits ductile and anisotropic characteristics under different pressure conditions. These investigated materials are suitable for use in optoelectronic devices due to their favorable physical properties under different pressure circumstances.