Vacancy effects on structural and electronic properties of 4d transition-metal carbides

We present a study of the effect of the vacancies on the structural and electronic properties in substoichiometric NbCx and MoCx in the NaCl type structure using ab-initio full-potential linear augmented plane wave method (FP-LAPW). A model structure of 8 and 16 atom supercell with ordered vacancies within the carbon sublattices is used. We find that the lattice parameters of the studied stoichiometries in both MoCx and NbCx are smaller than that of ideal stoichiometric MoC and NbC. Our results are found to be in good agreement with experiment and other theoretical ab-initio calculations.