Density functional theory study of Sc₈S₁₂ and Sm₈S₁₂ as photocatalysts for water splitting

In this paper, we report first-principles study of scandium sulphide, Sc₈S₁₂, and samarium sulphide, Sm₈S₁₂, to assess their suitability for photocatalytic water splitting. We have investigated the mechanical, dynamic, electronic, and optical properties and elastic anisotropy using the Vienna Ab initio Simulation Package (VASP). From the observed results, both RE chalcogenides Sc₈S₁₂ and Sm₈S₁₂ exhibit structural and thermodynamic stability as reflected by the complete absence of any imaginary phonon mode. Electronic structure calculations using PBE, DFT + U, HSE06, and MBJ functionals revealed semiconducting behaviour, with band gaps of 1.30 eV (PBE), 1.33 eV (DFT + U), 1.60 eV (HSE06), 1.60 and 0.780 eV (PBE), 0.75 (DFT + U), 1.30 eV (HSE06) and 1.30 eV (MBJ) for Sc₈S₁₂ and Sm₈S₁₂, respectively. To achieve accurate description of the optical response, the GW + BSE approach was applied, yielding absorption edges of 2.24 eV for Sc₈S₁₂ and 2.20 eV for Sm₈S₁₂, confirming their strong absorption in the visible region. Elastic constants revealed mechanical stability and anisotropy and direction-dependent optical spectra reflect the anisotropic nature of these compounds. Their integrated properties show that both materials are preferable for visible light-driven photocatalytic applications. These predictions need to be verified through experimental synthesis and characterisation to establish their stability and functional performance.