Stability Prediction of 2H–MoO ₂ Monolayer as a Platform for Photonic Devices: from Thermodynamics to the Excitonic Effects through First-Principles Calculations

The conception, study, and development of two-dimensional (2D) materials have expanded the frontiers of next-generation optoelectronic devices. Representative of this class, the MoO₂ monolayer in its 2H phase was investigated here with respect to its structural, electronic, optical, and excitonic properties, through the PBE level for structural and electronic properties, being the electronic band gap correct at the HSE06 level, the optical and excitonic properties were obtained by solving the Bethe-Salpeter equation. The structural stability was also investigated at the dynamical (phonons), thermodynamic (AIMD), and mechanical (elastic constants) levels, ensuring the stability of this monolayer at all levels. This 2D transition-metal dioxide exhibits semiconducting behavior with a HSE06 direct band gap of 2.50 eV, where spin-orbit coupling is weak. We also observe spin degeneracy breaking in the valence bands close to the Fermi level in the vicinity of the K and K' valleys and along the connecting path between them. Excitonic band-structure analysis revealed a binding energy of 0.38 eV, which gives rise to significant excitonic effects in the linear optical response. The response is isotropic across the infrared and visible ranges, extending to the onset of the ultraviolet spectrum.