Theoretical and Experimental Insights into Zero-Field Splitting of Edge Defects in Monolayer WSe₂*

Monolayer tungsten diselenide (WSe₂) is a compelling platform for quantum sensing and spin-based information technologies owing to its strong spin–orbit coupling, direct gap, and robust spin–valley physics. In our joint theory–experiment collaboration, defect-induced localized states in WSe₂ exhibit optically detected magnetic resonance (ODMR) signals, motivating a microscopic understanding of their zero-field splitting (ZFS). Here, we model edge-like defect configurations in WSe₂ monolayers using density functional theory (VASP) to emulate the long-diameter defects observed by our experimental partners. We compute spin-triplet ground states and extract ZFS tensors, revealing how the D and E parameters scale with defect geometry, coordination, and local symmetry breaking. Importantly, our calculated ZFS values and principal-axis orientations show quantitative trends consistent with our collaborators’ ODMR measurements, enabling assignment of candidate spin centers and clarifying the role of edge terminations. These results provide design rules for engineering stable, optically addressable spin defects in WSe₂ and point to tunable, scalable sensing modalities in 2D semiconductors.