First-Principles Calculations on Electronic Structures and Optical Properties of g-C3N4 Nanoribbons

The first-principles method based on density functional theory was performed to investigate the electronic structure and optical properties of the armchair nanoribbons (AC-g-C(3)N(4)NRs) and zigzag g-C3N4 nanoribbons (ZZ-gC(3)N(4)NRs). The results show that the edge H atoms of AC-g-C(3)N(4)NRs and ZZ-g-C(3)N(4)NRs can exist stably. The valence band maximums (VBMs) of AC-g-C(3)N(4)NRs are mainly contributed by most of N atoms, whereas the VBMs of ZZ-g-C(3)N(4)NRs are contributed by the N atoms near the CH edge. The conduction band minimums (CBMs) of AC-gC(3)N(4)NRs mainly belong to C and N atoms near the one edge or two edges of AC-g-C(3)N(4)NRs, while the CBMs of ZZ-gC(3)N(4)NRs mainly belong to C and N atoms near the NH edge of ZZ-g-C(3)N(4)NRs. The absorption coefficient and the reflectivity of AC-g-C3N4NR or ZZ-g-C3N4NR increased with the increasing width of the corresponding nanoribbon. An obvious blueshift phenomenon of the absorption coefficient could be generated in the low-energy range as the width of AC-g-C3N4NR increased.