Boundary conditions for transition-metal dichalcogenide monolayers in the continuum model

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We derive the boundary conditions for MoS₂ and similar transition-metal dichalcogenide honeycomb (2H polytype) monolayers with the same type of k·p Hamiltonian within the continuum model around the K points. In an effective 2-band description, the electron-hole symmetry breaking quadratic terms are also taken into account. We model the effect of the edges with a linear edge constraint method that has been applied previously to graphene. Focusing mainly on zigzag edges, we find that different reconstruction geometries with different edge-atoms can generally be described with one scalar parameter varying between 0 and 2π. We analyze the edge states and their dispersion relation in MoS₂ in particular, and we find good agreement with the results of previous density functional theory calculations for various edge types.