A first-principles method, which applied the local spin-density approximation to density-functional theory, was used to investigate the neutral substitutional N atom. The length of the unique extended N-C bond in the C3v-symmetry equilibrium structure was found to be 33% longer than the bond length in the bulk. The energy barrier to reorientation of this extended bond, between the 4 possible N-C bonds, was deduced to be 0.7eV. This value was in excellent agreement with experimental data.

S.J.Breuer, P.R.Briddon: Physical Review B, 1996, 53[12], 7819-22