Di-nitrogen-vacancy-hydrogen defects in diamond: a computational study

Density functional theory was used to determine selected experimentally observable properties of the N₂VH and N₂VH₂ point defects in diamond. We report that the symmetry of the defects are C_1h and C_2v respectively with the hydrogen(s) saturating carbon radicals that are produced when the vacancy is formed. N₂VH has an accessible negative charge state if the Fermi energy lies above around 2.4eV above the valence band top, as N₂VH₂ contains only species with their valence satisfied, only the neutral charge state of this species is thermodynamically stable. We predict that N₂VH⁰ would be detectable in infrared, with a C-H stretch mode around 3050 cm⁻¹ for the neutral species, shifting to 2700 cm⁻¹ in the negative charge state. N₂VH₂ is also expected to be visible in infrared, with the presence of two, sterically interacting H atoms resulting in peaks with higher wave numbers, being around 3370 and 3540 cm⁻¹ for the anti-symmetric and symmetric stretch modes, respectively. Similarities can be drawn between the bandstructures of N₂VH and the isoelectronic N₃V centre, from which we predict the likely electronic optical transition for this centre. N₂VH₂ is expected to not give rise to any sharp electronic transitions.