Electronic and structural properties of nitrogen-vacancy center in diamond nanocrystals: A theoretical study

Neutral and negatively charged nitrogen-vacancy centers in hydrogenated diamond nanocrystals are investigated including singlet and triplet spin states. The investigation is carried out using density functional theory at the generalized gradient approximation level of Perdew–Burke–Ernzerhof. Dilation and distortion in the direction of the N-Vacancy direction is observed. The smallest gap and the highest number of energy levels that enter the original unaltered forbidden energy gap are in the triplet state of the negatively charged nitrogen-vacancy center. Results show that the dipole moment and valance band width of the negatively charged nitrogen-vacancy center in the singlet state are the highest between investigated structures. Triplet state has the highest spin density at two carbon atoms near the nitrogen-vacancy with the remaining spin density at the nitrogen atom itself. For the neutral nitrogen-vacancy center the spin density nearly accumulates at one carbon atom near the nitrogen-vacancy only. Analysis of bonds and tetrahedral angles show that the present nitrogen-vacancy centers deviate appreciably from the ordinary structure of unaltered diamond nanocrystals.