Investigation of Strain Modulated Opto-Electronic Properties in Monolayer WX2 (X = Se and S): DFT and Beyond DFT Study

Abstract

This study explores the potential applications of 2H-WX₂ (X = Se, S) monolayers, which belong to the transition metal dichalcogenides—a class of 2D materials. Utilizing first-principles calculations with PBE and SCAN functionals, the study highlights the superior performance of SCAN-based functionals. The SCAN functional, a meta-GGA (generalized gradient approximation), offers greater accuracy by incorporating constraints based on known physical properties. This leads to better optimization of monolayer structures and closer agreement with experimental lattice constants and band gap values compared to the more commonly used PBE functional. This distinction underscores the scientific impact of using SCAN for studying these materials. The implication of using the SCAN with rvv10 functional suggests either a slight presence or no significant presence of long-range van der Waals interactions in these TMDC monolayers. The hybrid functional (HSE06) closely replicates the experimental band gap, while the GW approximation (GoWo) validates the experimentally known valence band splitting in these monolayers. The Bethe-Salpeter equation is subsequently solved to precisely explore the optical properties of these monolayers. Upon the application of uniaxial tensile strain, the absorption peaks gradually shift towards lower energy regions. Additionally, these monolayers exhibit a transition from a direct to an indirect bandgap under critical strain, making them suitable candidates for optoelectronic devices, photodetection, sensing, and flexible electronics.