First-principles investigation of Be3PX3 (X = F, Cl, Br) halide anti-perovskites: structural stability, optoelectronic properties, and theoretical photocatalytic screening.

In this work, a comprehensive first-principles investigation of Be3PX3 (X = F, Cl, Br) anti-perovskites is performed using density functional theory (DFT) within the CASTEP framework to explore their structural, electronic, optical, and photocatalytic properties. The optimized structures satisfy the investigated mechanical and dynamical stability criteria, while the energetic analysis indicates favorability against the selected decomposition pathway. Electronic band structure analysis reveals indirect E g of 4.59 eV, 1.01 eV, and 0.29 eV (HSE06) for Be3PF3, Be3PCl3, and Be3PBr3, respectively, indicating strong tunability across the series. Band-edge alignment analysis suggests that Be3PF3 meets the theoretical redox criteria for overall water splitting based on preliminary electronic-structure screening. However, further studies on aqueous chemical stability, surface reactions, pH effects, and experimental validation are required to evaluate its practical photocatalytic potential. The calculated low effective masses indicate favorable carrier transport tendencies, while the low exciton binding energies (2.1-11.0 meV) suggest efficient exciton dissociation and potential for improved charge separation. The combined tunability of the bandgap, optical response, and carrier dynamics highlights the potential of Be3PX3 (X = F, Cl, Br) compounds for ultraviolet-to-visible optoelectronic applications. Among the investigated compounds, Be3PF3 shows favorable band-edge alignment for overall water splitting, although its wide bandgap restricts absorption mainly to the UV region. Additionally, the materials demonstrate good mechanical stability and low thermal conductivity, supporting their suitability for durable device applications.