Interface energy and electron structure for Fe/VN

The electronic and atomic structures in a model system of the semicoherent interface between bcc-Fe and nacl-VN is studied. Knowledge of interface structure and energetics is important for modeling of nucleation and growth in complex alloys on a thermodynamical level. Present model system is of interest, as Such interfaces are common in alloyed steels. For the total energy calculation a pseudopotential (PP) implementation of density-functional theory (DFT) is used. In particular, the code includes ultrasoft PP and the so-called generalized-gradient approximation (PW91) for the DFT exchange and correlation energy. We have calculated interface energies for supercells with a varying VN unit thickness and, in addition to the ideal interface, also interfaces with N vacancies are considered. The Fe/VN interface energy is found to be very small, although the presence of vacancies raises the energy. Experimentally observed VN precipitates are very thin and the calculations point out features of the electron structure that make this smallness favorable.