First-principles calculation and molecular dynamics simulation of fracture behavior of VN layers under uniaxial tension

We develop the second nearest-neighbor modified embedded atom method (2NN MEAM) potential for vanadium nitride (VN) in terms of the individual vanadium and nitrogen. The potential parameters are determined by fitting the cohesive energy, lattice parameter, and elastic constants of the VN with the NaCl-type structure, which are obtained by first-principles calculations. We find that the developed potentials can be used to describe the fundamental physical properties of the V-N system with other lattice structures. The calculated tensile stress-strain curves of the VN layers by first principles agree with those obtained by molecular dynamic simulations, validating the use of the developed potential. The bond breaking and its growth and coalescence are found to play an important role in the formation of fracture. We also find that temperature influences markedly the breaking of bonds, which can be attributed to the deviation of atoms from their equilibrium positions due to the thermal activated vibration, or to the superposition of the thermal energy to the deformation energy. Moreover, no dislocations and slips are found throughout the deformation process.