Stability and mechanical properties of C2N2X (X=O, NH and CH2) from first-principles calculations

The structural stability and mechanical properties such as elastic constants, mechanical moduli, Vickers hardness and mechanical anisotropy of C2N2X (X=O, NH and CH2) are calculated by first principles calculations based on the density functional theory. The calculated lattice parameters, elastic constants of C2N2X (X=O, NH and CH2) are in good agreement with the experimental data and previous calculated values. C2N2X (X=O, NH and CH2) are also found to be thermodynamically and mechanically stable. The mechanical moduli (bulk modulus, shear modulus and Young's modulus) are evaluated by Voigt–Reuss–Hill approach. The hardness of C2N2X (X=O, NH and CH2) is calculated using both the ab initio and semiempirical model calculations. The Vickers hardness of C2N2X (X=O, NH and CH2) is approximate to 40 GPa of the superhard materials. In conclusion, these materials can be regarded as potential candidate of ultra-incompressible and hard materials. Furthermore, the mechanical anisotropy is also discussed in details