Band gap of C3N4 in the GW approximation

Abstract Ab initio calculations based on density functional theory are performed to study the stability of newly proposed C 3 N 4 forms. Heptazine-based g-C 3 N 4 was found to be energetically favored relative to other phases. The quasiparticle band energies of different C 3 N 4 phases are calculated using the GW method. Among the seven phases of C 3 N 4 studied, only the pseudocubic phase and g-h-triazine phase have direct band gaps, and all of the other phases have indirect band gaps. The band gap of α-C 3 N 4 , β-C 3 N 4 , cubic-C 3 N 4 , pseudocubic-C 3 N 4 , g-h-triazine, g-o-triazine and g-h-heptazine is 5.49 eV, 4.85 eV, 4.30 eV, 4.13 eV, 2.97 eV, 0.93 eV and 2.88 eV, respectively. From the viewpoint of band gap energies, both the g-h-heptazine and the g-h-triazine phases can be used as suitable photocatalysts for hydrogen production using water.