Investigating structural, vibrational, electronic, and optical properties of W₀.₅Mo₀.₅S₂ₓSe₂(₁₋ₓ) layered quaternary alloys using Ab initio for optoelectronic applications

This study investigates the structural, vibrational, electronic, and optical properties of W and S co-substituted W₀.₅Mo₀.₅S₂ₓSe₂(₁₋ₓ), where x = 0.25, 0.50, and 0.75) alloy compositions for optoelectronic applications. Employing first-principles calculations through the Quantum Espresso platform, we investigated how incorporating W and S influences the hexagonal crystal structure of 2H-MoSe₂. The study demonstrates that the simultaneous substitution of W and S notably affects the material’s properties, including lattice parameters, bandgap, and optical absorption (extinction coefficient). The calculated equilibrium lattice parameters for both 2H-MoSe₂ and W/S co-substituted materials show strong agreement with experimental results and previously reported theoretical data. In the phonon spectra, the absence of negative frequencies in W₀.₅Mo₀.₅S₂ₓSe₂(₁₋ₓ) indicates that the material is dynamically stable. The calculated bandgaps of these layered materials are lower than the experimental bandgap of the unsubstituted material, indicating enhanced favorability for optoelectronic applications. Additionally, we computed the average isotropic optical properties across all systems and excluded SOC due to its negligible effect on the electronic properties and the high computational cost it entails. The Penn model provides an accurate description for both 2H-MoSe₂ and W₀.₅Mo₀.₅S₂xSe₂(1−x) systems.