(color online) (a) Band structure of nanoribbon of As–Cl. Size of red solid circle represents the contribution of X edge atoms within two unit cells from two edges. Size of blue solid circle represents the contribution of interior atoms. Symbol size indicates the contribution weight. Inset shows a magnified part of the edge states around the Γ point. (b) Diagram of nanoribbon and the real space projection of wave functions at the Γ point.