Pressure-induced evolution of the electronic structure and band gap expansion in MgPbN2

The structural, electronic, and optical properties of MgPbN2 under pressure have been systematically studied using first-principles calculations combined with the CALYPSO crystal structure prediction method. Two ambient pressure phases (Pna21 and I-42d) and two high-pressure phases (R-3m and Fd-3m) were identified, all of which are dynamically, mechanically, and thermally stable, and exhibit semiconductor characteristics. Notably, their band gaps increase with increasing pressure. This phenomenon is primarily attributed to two factors. First, the strengthened orbital coupling under pressure enhances electron cloud overlap, raising the energy of antibonding states (conduction band) and lowering the energy of bonding states (valence band). Second, high pressure alters the distribution of electron clouds, causing electrons to become more localized around the atoms. This localized electron distribution reduces electron transitions between energy bands, thereby increasing the band gap. This analysis provides a unified view of the electronic structure evolution under compression, linking microscopic orbital interactions to macroscopic observable properties. The calculations and analysis of the optical absorption and reflectivity coefficient suggest that the two high-pressure phases of MgPbN2 have potential applications in transparent optics and ultraviolet detection. This study provides insights into the role of pressure in tuning optical properties.