Edge reconstruction of 2D-Xene (X = Si, Ge, Sn) zigzag nanoribbons

By performing first principles calculations, we investigate the edge reconstruction in free-standing 2D-Xene (X = Si, Ge, Sn) zigzag nanoribbons. Three different periodicities of edge reconstruction (2a,3a,4a) are found, in which the reconstruction with 3a periodicity has the lowest energy and shows non-magnetic ground state. The edge reconstruction can be understood by the reconfiguration of the dangling bond states and edge states at the zigzag edges. Due to the structural buckling, extra bonding states are formed between edge atoms and inner atoms, accompanied with charge transfer from the edge states to the dangling bond states. This results in one-third occupied dangling bond states and a Peierls-like structural reconstruction with 3a periodicity at the edge which opens a small band gap. With a tight binding model, the reconstruction of the electronic structures at the edges are revealed by the hopping integrals between different edge X-p orbitals.