  Recently, Bafekry et al. [Appl. Phys. Lett. 119, 142102 (2021)] reported
their density functional theory (DFT) results on the elastic constants of a
novel C6N7 monolayer. They predicted a very soft elastic modulus of 36.29 GPa
for the C6N7 monolayer, which is remarkably low for carbon-nitride 2D lattices.
Using DFT calculations, we predict a remarkably higher elastic modulus of 267
GPa for this monolayer. The maximum tensile strength is also predicted to be
20.5 GPa, revealing the outstanding mechanical properties of the C6N7
monolayer.
