Substitutional boron and nitrogen pairs in diamond. A quantum mechanical vibrational analysis

The lattice structures, electronic characteristics and spectroscopic features of the three vicinal substitutional, spin zero defects, N _s -N _s (A-centre), B _s -B _s , and B _s -N _s in diamond are reported. They are derived from all-electron B3LYP calculations based on Gaussian basis sets, within a periodic supercell scheme, including both 64- and 216-atom cells. The local geometry reflects the differences between the strong C-C bond of the host lattice and the weaker impurity-impurity bonding in the defective systems. The band structures show two occupied bands 1.06 eV above the VBE for N _s -N _s , and empty bands 3.36 eV and 0.25 eV below the CBE for B _s -B _s and for B _s -N _s respectively. The IR spectra of B _s -B _s and N _s -N _s contain sharp peaks at 631 cm ⁻¹ , 692 cm ⁻¹ and 1373 cm ⁻¹ , and 451 cm ⁻¹ , 571 cm ⁻¹ and 1276 cm ⁻¹ , respectively, which might reasonably be considered as ‘finger prints’ for these systems. For B _s -N _s , a set of medium intensity absorptions are predicted at 890 cm ⁻¹ , 945 cm ⁻¹ , 1018 cm ⁻¹ , 1078 cm ⁻¹ and 1281 cm ⁻¹ . However, numerous peaks in this region have been predicted for other defective systems, so that the firm identification of B _s -N _s based on these frequencies is much less certain than B _s -B _s and N _s -N _s .