(a) Basis sites in a unit cell of centrosymmetric puckered α structure. (b) 2D rectangular BZ with Dirac points marked by red dots. A pair of type-I Dirac points are marked as D and D′ on Γ–X₂, while two pairs of type-II Dirac points are marked (red dots) near F and F′ on Γ–X₁. (c) Schematic energy dispersions around D and F points respectively illustrating type-I and type-II Dirac points. (d) Band structures of 2D phosphorene (α phase with h = 0) type lattice structure of group-V elements in the absence of SOC, the red and green dots size shows the projection on the p_z (p_x) atomic orbitals.^[78]