Fig. 1. (Color online) (a) The crystalline structures and (b) 2D charge density difference plot of C₅₆₈. The square unit-cell marked in green line, where a and b represent unitcell vectors.

Fig. 2. (Color online) The band structures and projected density of states of C₅₆₈, with the Fermi level are set to zero. The charge densities of several key states are also presented.

Fig. 3. (Color online) Band structures of C₅₆₈ with different uniaxial strains, with the Fermi level set at zero and marked with the black dashed line. Positive and negative values of strains indicate tensile and compressive cases, respectively.

Fig. 4. (Color online) (a) Band gap, (b) band edge position, (c) optical absorption, and (d) effective mass of C₅₆₈ with different uniaxial strains. CBM_Γ and CBM_M are the conduction band minimum at Γ and M points. The vacuum level is taken as the zero energy reference in (b).

Fig. 5. (Color online) Band structures of C₅₆₈ with different biaxial strains, with the Fermi level set at zero and marked with blacked dashed line. Positive and negative values of strains indicate tensile and compressive cases, respectively.

Fig. 6. (Color online) (a) Band gap, (b) band alignment, (c) optical absorption, and (d) effective mass of C₅₆₈ with different biaxial strains. CBM_Γ and CBM_M are the conduction band minimum at Γ and M points. The vacuum level is taken as the zero-energy reference in (b).