Ab initio calculations of structural, phonon, thermal, electronic, and optical properties of W x Mo1− x S2 y Se2(1− y ) materials for x = 0, 0.125; y = 0.0625, 0.125

This ab initio computational study investigates the structural, vibrational, thermal, electronic, and optical properties of tungsten and sulfur-doped molybdenum diselenide alloys (WxMo1−xS2ySe2(1−y)). All doped structures demonstrate dynamic stability, and their calculated lattice constants show strong agreement with experimental data. Thermodynamically, the system behaves as expected: the Helmholtz free energy declines sharply with increasing temperature, consistent with the third law of thermodynamics. Notably, the composition with x = y = 12.5% exhibits the narrowest bandgap, enabling enhanced broadband light absorption. Moreover, key optical responses, including the dielectric function, absorption coefficient, and refractive index, are highly tunable via doping concentration, underscoring the material’s promise for customizable optoelectronic devices. These findings provide a robust theoretical basis for engineering next-generation semiconductors with tailored functionalities for energy and photonic applications.