A density functional theory study of nitrogen vacancy center in lonsdaleite

Lonsdaleite is a carbon allotrope and metastable form of diamond that demonstrates superior mechanical properties over cubic diamond. Here, we report the results of density functional theory (DFT) and molecular dynamics (MD) studies of neutral and negative nitrogen vacancy (NV) centers in lonsdaleite. Interestingly, the neutral (NV⁰) and negative (NV⁻¹) nitrogen vacancy centers in lonsdaleite display a remarkable splitting between the two degenerate e_x and e_y excited states nearly around ∼0.5 eV for NV⁰ and 0.2 eV for NV⁻¹, respectively. The thermal stability, dynamic stability, band structure, density of states, and optical properties are computed. DFT and MD calculations reveal that the geometrical structure of the NV center in lonsdaleite is both thermally and dynamically stable. In addition, the findings show that NV⁰ and NV⁻¹ centers in lonsdaleite demonstrate splitting in the zero-phonon line (ZPL) due to symmetry reduction from C_3v to C_1h with respect to the NV center in cubic diamond. Furthermore, the results indicate that ZPL falls around ∼1.76 and 2.25 eV for NV⁰, whereas it lies around 1.91 and 2.19