Structural stability and tunable optoelectronic properties of 2H-Mo1-xVxS2 monolayers (x = 0, 0.25, 0.50, and 0.75): A first-principles investigation

This work presents a first-principles investigation of the structural, energetic, optoelectronic, and dynamical properties of pristine and V-substituted 2H-MoS2 monolayers, with V substitution concentrations of 25%, 50%, and 75%. Density functional theory (DFT) within the generalized gradient approximation (GGA), together with the Heyd–Scuseria–Ernzerhof screened hybrid exchange-correlation functional (HSE06), density functional perturbation theory (DFPT), and ab initio molecular dynamics (AIMD), was employed to observe the effects of V incorporation. The optimized structures retain the characteristic layered framework, while the in-plane lattice parameter varies from 3.185 to 3.197 Å and the layer thickness decreases from 3.127 Å for pristine MoS2 to 2.92 Å at 75% V substitution, indicating concentration-dependent structural relaxation and enhanced V–S interactions. The energetic analysis reveals negative formation energies of −0.867, −0.861, and −0.862 eV for the 25%, 50%, and 75% V-substituted systems, respectively, compared with −0.890 eV for pristine MoS2, indicating favorable formation with respect to the adopted reference states. The positive cohesive energies of 6.1627, 6.4840, and 6.2764 eV further demonstrate substantial atomic binding within the substituted monolayers. Phonon calculations and AIMD simulations at 300 K support the dynamical and thermal stability of the investigated structures. V substitution gradually narrows the electronic band gap from 1.6758 eV for pristine MoS2 to 1.361, 1.1879, and 1.053 eV for 25%, 50%, and 75% V substitution, respectively, primarily due to the introduction and redistribution of V-3d states and their interaction with Mo-d and S-p orbitals. This electronic reconstruction produces a pronounced redshift in the optical absorption edge from 1.131 to 1.02 eV and enhances the low-energy dielectric response with increasing V concentration. The combined structural, energetic, and optoelectronic results demonstrate that substitutional V incorporation offers an effective route for tuning the properties of MoS2 monolayers while retaining promising energetic and structural stability, highlighting their potential for tunable optoelectronic applications.