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.