The NV⁰ defects in diamond: A quantum mechanical characterization through its vibrational and Electron Paramagnetic Resonance spectroscopies

The NV⁰ defect in diamond has been investigated quantum-mechanically, by analyzing its structural, electronic, vibrational and magnetic properties. The possible spin states for NV⁰ are a quartet NV_q⁰ (⁴A₂ symmetry) and a doublet (²E symmetry). In the latter state a single electron occupies a double degenerate level producing a Jahn Teller distortion that removes the degeneracy and lowers the total energy. The symmetry reduces from C_3v to C_S and two local minima are indeed identified, to be indicated as NV_d1⁰ (²A′ symmetry) and NV_d2⁰ (²A″ symmetry). NV_d1⁰ is the ground state, and is more stable than NV_q⁰ by ~ 0.5 eV, and than NV_d2⁰ by ~ 0.2 eV, irrespective of the functional or basis set adopted. The EPR hyperfine coupling tensor has been computed for NV_q⁰ and has been found to be in excellent agreement with available experimental data. The IR spectra of the NV defects (the three neutral cases and also the negatively charged one, for comparison) show specific peaks and shape that characterize each system and differentiate the spectra according to the spin and charge state. The Raman spectra of the NV⁰ defects shows a single peak, redshifted with respect to the single peak of pristine diamond by 2 cm⁻¹ only, but in turn well separated from the negatively charged form of the defect.