First-principles investigation of high pressure Pbca phase of carbon mononitride

• Pbca-CN is stable up to at least 100 GPa.
• Pbca-CN exhibits a large elastic anisotropy.
• Pbca-CN is an ultra-incompressible material.
• The ideal strength calculations show that Pbca-CN is not an intrinsic superhard material.

A theoretical investigations on the stability, mechanical and electronic properties of Pbca-CN was performed by using first principle calculations. According to our calculations, Pbca-CN exhibits a large elastic anisotropy. The further mechanical calculations demonstrated that Pbca-CN shows high elastic moduli. Young's modulus of Pbca-CN is found to reach a maximum along [001] direction and a minimum along [100] direction. The ideal tensile and shear strength at large strains of Pbca-CN are also examined. The ideal shear strength along the weakest (100)[010] slip system is about 20 GPa, which shows Pbca-CN is not an intrinsic superhard material.