Based on density functional theory calculations,it is found that for substitutional N in diamond the C3v symmetry structure is more stable,while C3v and D2d symmetry pattes for the substitutional P in diamond have comparable energies.Moreover,the substitutional N is a deep donor for diamond,while P is a shallow substitutional n-type dopant.This is attributed to the different doping positions of dopant (the N atom is seriously deviated from the substitutional position,while the P atom nearly locates in the substitutional site),which are determined by the atomic radius.