Mechanical properties and electronic structures of VC, V4C3and V8C7from first principles

The lattice parameters, elastic properties, electronic structures and hardness of VC, V4C3 and V8C7 were studied by means of the pseudo-potential plane-waves method using the density function theory (DFT). The present lattice parameters of VC, V4C3 and V8C7 agree well with other theoretical and experimental data. V4C3 and V8C7 have lower values than VC in bulk modulus, shear modulus and Young's modulus, respectively. According to the analysis of the density of states of VC, V4C3 and V8C7, it was found that a C vacancy leads to the emergence of new peaks near the Fermi level that give a negative contribution to the shear modulus. As the hardness cannot be calculated from DFT directly, a semi-empirical model was used to estimate the hardness. Based on the overlap populations and bond lengths obtained from DFT, the hardness values of VC, V4C3 and V8C7 were evaluated. Furthermore, VC has the highest hardness.