ScBr₂/AlSe: a magnetic dihalide/non-magnetic chalcogenide van der Waals heterostructure from first principles

Combining intrinsic 2D ferromagnetism with a broadband optoelectronic response within a single van der Waals (vdW) architecture remains an open design challenge. Here, first-principles density-functional-theory calculations are used to investigate the ScBr₂/AlSe vdW heterostructure, representing the first coupling of a magnetic transition-metal dihalide with a non-magnetic group-III chalcogenide. The low lattice mismatch (δ ≈ 2.17%) yields three energetically near-degenerate stacking configurations within PBE+D3 accuracy; the heteroB stacking is adopted as the representative geometry and its dynamical, thermal and mechanical stability is confirmed through phonon dispersion, machine-learned-force-field-accelerated ab-initio molecular dynamics at 300 K, and Born-stable elastic constants. HSE06 calculations yield a direct gap of 0.57 eV with clear Type-II band-edge character, and the ScBr₂ magnetic moment is preserved at 1.0 µB per Sc atom. The optical response shows strong absorption across the visible and ultraviolet regions with in-plane isotropy. These results establish the transition-metal-dihalide/group-III-chalcogenide class as a promising design space for multifunctional magnetic–optoelectronic vdW heterostructures.