A first-principles theoretical study on two-dimensional MX and MX$_2$ metal halides: bandgap engineering, magnetism, and catalytic descriptors

Metal halides, particularly MX and MX$_2$ compounds (where M represents metal elements and X = F, Cl, Br, I), have attracted significant interest due to their diverse electronic and optoelectronic properties. However, a comprehensive understanding of their structural and electronic behavior, particularly the evolution of these properties from bulk to low-dimensional forms, remains limited. To address this gap, we performed first-principles calculations to develop a database of 60 MX and MX$_2$ metal halides, detailing their structural and electronic properties in both bulk and slab configurations. Calculations were performed using the advanced \texttt{HSE06-D3} hybrid functional for density functional theory (DFT), ensuring high precision in predicting material properties despite the associated computational cost. The results reveal that these materials are predominantly semiconductors, but their bandgaps range from 0 to 9 eV. A detailed analysis of the transition from bulk to slab structures highlights notable shifts in electronic properties, including bandgap modifications. Upon dimensional reduction, 9 materials exhibit an indirect-to-direct bandgap transition, enhancing their potential for energy conversion. Beyond structural dimensionality, the influence of chemical composition on bandgap variations was also examined. To further assess their practical applicability, the catalytic and magnetic properties of these metal halides were systematically evaluated. These findings not only illuminate previously underexplored MX and MX$_2$ metal halides but also identify promising candidates for electronic, optoelectronic, catalytic and spintronic applications. This database serves as a valuable resource for guiding future research and technology development in low-dimensional materials.