Formation energy, mechanical and electronic properties of buckled heptazine ([formula omitted]) sheet: First-principles calculations

Abstract

Using first-principles calculations based on density functional theory (DFT) the formation energy (EFE), elastic constants, elasticity and electronic property of buckled heptazine C6N8 sheet are examined. The calculated negative EFE (-0.34 eV) confirms the experimental synthesis of the buckled C6N8 sheet. It is revealed that the obtained in-plane stiffness (Yx/Yy) along the x (90.48 N/m) and y- (100.25 N/m) are lower than that of planar heptazine (212.46 N/m) and striazine (133.55 N/m) sheets. The decrease in rigidity is mainly due to the bonding nature of the sheet causing softening for the buckled hexagonal rings and hardening for the planar rings. The calculated Poisson's ratio (vx/vy) is 0.166/0.183 which is larger than that reported for planar heptazine (0.10) and striazine (0.08) sheets. The bulk modulus (57.8 N/m) of buckled C6N8 sheet is about half the value to that of planar heptazine sheet (108.01 N/m). The estimated values of the critical strains (elastic and yielding) points show that the buckled C6N8 sheet cannot withstand larger tensions as compared with the planar heptazine sheet. These results established a stable mechanical property for the buckled C6N8 sheet. Also the buckled C6N8 sheet exhibits intrinsic semiconducting property with an indirect band gap of 1.85 eV. These noble physical properties can be useful in carbon-based nanosheet applications.