The electronic and structural properties of N-doped amorphous material were studied by using  ab initio  total energy calculations. It was found that the 3-fold coordinated N impurity (N3) and the 4-fold coordinated N impurity (N4) exhibited negative effective Coulombic interactions. An analysis of the results showed that the electrical effect of n-type doping, due to N atoms, was not related only to chemical equilibrium between N3 and N4.

P.P.M.Venezuela, A.Fazzio: Physical Review Letters, 1996, 77[3], 546-9