This study used the first-principles-based CASTEP software to calculate the structural, electronic, and optical properties of heterojunctions based on single-layer GaN. GaN-MX₂ exhibited minimal lattice mismatches, typically less than 3.5%, thereby ensuring lattice coherence. Notably, GaN-MoSe₂ had the lowest binding energy, signifying its superior stability among the variants. When compared to single-layer GaN, which has an indirect band gap, all four heterojunctions displayed a smaller direct band gap. These heterojunctions were classified as type II. GaN-MoS₂ and GaN-MoSe₂ possessed relatively larger interface potential differences, hinting at stronger built-in electric fields. This resulted in an enhanced electron–hole separation ability. GaN-MoSe₂ exhibited the highest value for the real part of the dielectric function. This suggests a superior electronic polarization capability under an electric field, leading to high electron mobility. GaN-MoSe₂ possessed the strongest optical absorption capacity. Consequently, GaN-MoSe₂ was inferred to possess the strongest photocatalytic capability. The band structure and optical properties of GaN-MoSe₂ under applied pressure were further calculated. The findings revealed that stress significantly influenced the band gap width and light absorption capacity of GaN-MoSe₂. Specifically, under a pressure of 5 GPa, GaN-MoSe₂ demonstrated a significantly narrower band gap and enhanced absorption capacity compared to its intrinsic state. These results imply that the application of stress could potentially boost its photocatalytic performance, making it a promising candidate for various applications.

This study calculates the electronic structure and optical properties of intrinsic BiOIO₃ and X-BiOIO₃ (X = As, Se, or Te) using PBE (Perdew–Burke–Ernzerhof) and MBJ (Modified Becke–Johnson) functionals based on density functional theory, with MBJ showing better correlation with experimental values. The X-BiOIO₃ systems exhibit relative stability under MBJ potential and show crystal lattice distortion compared to intrinsic BiOIO₃, creating localized potential differences that enhance polarization and adjust the bandgap. Doping reduces the bandwidth and increases energy level density, promoting electron transitions. Consequently, based on the computational results presented in this paper, it can be inferred that both BiOIO₃ and X-BiOIO₃ facilitate water hydrolysis and oxygen generation due to their favorable energy band positions. Notably, Se-BiOIO₃ exhibits the highest visible light absorption capacity, which may enhance photocatalytic efficiency by strengthening the built-in electric field and promoting charge carrier generation.