(a) Side and top views of α-Bi ML with buckling. The upper and lower atomic layers are presented in blue and green colors, respectively. The buckling height h is defined by the distance between the atoms within the same ML. (b) The h-dependent energy gap (Δ) at Dirac point of α-Bi ML. (c) Band structures of non-buckled (h = 0) α-Bi without and with SOC as well as buckled α-Bi with SOC at different buckling heights (h = 0.1 Å and 0.5 Å).^[73]