N-vacancy defects in c-BN and w-BN

Using the ab initio Hartree-Fock method in the molecular-cluster approach the neutral and doubly-positively charged N-vacancy in cubic boron nitride (c-V-[N], c-V-[N](+2)) and in neutral wurtzite boron nitride (w-V-[N]) are studied. For all cases, after a total energy minimization, a C-3v local symmetry configuration is found. A charge trapped in the nitrogen vacancy is obtained resembling a F-center-type defect, like in alkali-halides. The possible role played by this F-center-type defect in the interpretation of EPR signals is discussed.