A first-principles study of orthorhombic CN as a potential superhard material.

Using first-principles calculations, we have investigated the structural, electronic, dynamical and mechanical properties of a recently synthesized Pnnm-CN. Phonon dispersion and elastic constant calculations were carried out to demonstrate the dynamical and mechanical stabilities of the Pnnm structure of CN at ambient pressure. The electronic band structure suggests that Pnnm-CN is an insulator with an indirect band gap of about 3.7 eV. First-principles strain-stress relationships at large strains were also simulated to examine the structural and mechanical properties of Pnnm-CN. The established ideal tensile strength of ∼41 GPa in the 〈100〉 direction suggests that CN is a potential superhard material. The present results provide deep insights for understanding the mechanical properties of CN and thus are helpful to explore the potential industrial applications of CN.