Computational Exploration of Structural, and Stabilities, Electronic, Optical and Photocatalytic Properties in Rare-sulfides Containing Halides YSX (X = F, and Br)

This study explores YSX (X = F, Br), a rare-earth sulfide-halide compound, as a photocatalytic material for renewable hydrogen energy using density functional theory (DFT) with the projector-augmented-wave (PAW) method and a meta-GGA potential. Structural relaxations using the PBE functional yielded lattice parameters of a = b = 3.73443 Å and c = 6.77194 Å, and unit-cell volume (V = 94.44 Å3) for tetragonal YSF, and a = 6.66456 Å, b = 6.81165 Å, and c = 13.07640 Å, and (V = 593.62 Å3) for orthorhombic YSBr. We tested the stability of these compounds using elastic and phonon stability and confirmed that both are mechanically and dynamically stable. Electronic band structures calculated with the TB-mBJ potential reveal direct band gaps of 2.06 eV and 2.54 eV for YSF and YSBr at the gamma point, respectively, and indicate that the compounds are semiconductors. Optical properties calculated from HSE06+BSE further reveal the semiconductor characteristic, with YSF at 2.22 eV and YSBr at 2.59 eV, as reported Tauc plot optical gaps. The calculated electron effective mass (Me) is 0.30 me and 0.59 me, and the hole effective mass (Mh) is 1.89 me and 1.17 me, revealing good electron and moderate hole mobility for YSF and YSBr, respectively. Calculated conduction and valence band edges (ECB) of +0.30 V and -0.48 V, and (EVB) of +2.52 V and +2.12 V for YSF and YSBr, respectively, indicated that YSBr is thermodynamically feasible for photocatalytic water splitting.