First principles investigation of the electronic properties of graphitic carbon nitride with different building block and sheet staggered arrangement

Highlights: • The electronic properties of g-C₃N₄ are investigated systematically. • The thermodynamic properties of g-C₃N₄ are also calculated. • The band gaps of monolayer sheets are larger than those of bulk counterparts. • The building block and sheet staggered arrangement affect the electronic properties. The electronic properties of g-C₃N₄ with different building block and sheet staggered arrangement are studied by using first-principles calculations. The calculated lattice constants and band gaps of bulk g-C₃N₄ with different space group P-6m2, R3m, Cmcm and P6₃/mmc consistent well with the previous results. The hybrid functional HSE06 is performed to evaluate the electronic properties of graphitic carbon nitride, and it is suggested that the HSE06 hybrid functional could predict more reasonable band gap than the traditional functional. The band gaps of bulk g-C₃N₄ with P-6m2, R3m, Cmcm and P6₃/mmc structure are about 2.8 eV, 2.6 eV, 2.6 eV and 2.4 eV, respectively. The electronic properties of monolayer triazine- and heptazine-based structure for g-C₃N₄ are also studied, and the corresponding band gaps are 3.0 eV and 2.7 eV, respectively. Compared to the monolayer g-C₃N₄, the decreasing band gaps of bulk structures should be attributed to the band overlapping among the neighboring graphitic CN sheets. The thermodynamic properties of bulk g-C₃N₄ are also investigated, and the results show that the heptazine-based structures have larger thermal expansion coefficient and relatively smaller thermal conductivity compared to the triazine-based structures. These calculated results are suggested that not only building block but also sheet staggered arrangement has important effect on the electronic properties of g-C₃N₄. Furthermore, the charge density of monolayer g-C₃N₄ shows that C and N atoms of g-C₃N₄ sheets with different building block are all sp² hybridization, which is similar to that of graphite. Our results unveil that the building block and sheet staggered arrangement are effective factors to tune the electronic structure and enhance the sunlight absorption efficiency of g-C₃N₄.