Topological Origin of Intrinsic High Chern Numbers in Two-Dimensional M₂X₂ Materials

Despite sharing a common lattice structure, monolayer M₂X₂ compounds realize quantum anomalous Hall phases with distinct Chern numbers, a striking phenomenon that has not been fully exploared. Combining first-principles calculations with symmetry analysis and tight-binding models, we identify two generic band-inversion mechanisms governed by the orbital composition and symmetry representations of 3d states near the Fermi level. When dxz/dyz orbtials dominate, a doubly degenerate $Γ$-point inversion yields $C=1$; otherwise, inversions occur along $Γ$-X and $Γ$-Y at four C₄-related momenta, whose Berry-curvature contributions add to give $C=2$, distinct from scenarios relying on multiple bands inversions at a single k point. The same mechanism consistently explains related two-dimensional systems, including LiFeSe, KTiSb, MgFeP, and Janus M₂X₂ derivatives. The mechanism provide practical guidance for screening and engineering tunable high-Chern-number insulators.