Abstract
The effect of the nitrogen vacancy on the bonding in the VNx crystal is investigated by means of the CNDO/2 cluster calculations. It is shown that the existence of the N vacancy leads to local lattice relaxation and rearrangement of the interatomic bonds in its neighbourhood. One of the most interesting results is the appearance of strong V-V bonds through the vacancy site. The presence of the vacancy leads to the lowering of the total energy of the cluster and stabilization of the defect phase.