  Recently, Bafekry et al. [Appl. Phys. Lett. 120, 189901 (2022)] reported
their density functional theory (DFT) results on the elastic constants of C6N7
monolayer. They predicted non-zero elastic constants along the out-of-plane
direction for a single-layered material, which contradicts with basic physics
of the stiffness tensor for plane stress condition. Moreover, in their work
Young's modulus is erroneously calculated. On the basis of DFT calculations,
herein we predicted the C11, C12 and C66 of the C6N7 monolayer to be 286, 73
and 107 GPa, respectively, equivalent with an in-plane Youngs modulus of 267
GPa. Using DFT calculations and a machine learning interatomic potential, we
also show that C6N7 monolayer shows isotropic elasticity.
