The search for a band of a defect predicted above 4000 cm−1 in diamond through infrared vibrational spectra: a quantum mechanical investigation

Abstract

For many years, the atomic structures of several defects in diamond with high wavenumber (>4000 cm⁻¹), including “amber centers”, H1b, and H1c, have been investigated, but a conclusive explanation is still lacking. In this paper, we propose a novel model for the N–H bond under repulsion, with an expected vibrational frequency exceeding 4000 cm⁻¹. Additionally, potential defects called NVH₄ are proposed to investigate their correlation with these defects. Three NVH₄ defects are considered, denoting a charge of e = +1, e = 0, and e = −1 for NVH₄⁺, NVH⁰₄, and NVH₄⁻, respectively. Subsequently, the geometry, charge, energy, band structure, and spectroscopic characterization of the three defects NVH₄⁺, NVH⁰₄, and NVH₄⁻ are analysed. Then, the calculated harmonic modes of N₃VH defects are used as a benchmark for studying NVH₄. The simulations indicate that, with the use of scaling factors, the highest NVH₄⁺ harmonic infrared peaks are 4072 cm⁻¹, 4096 cm⁻¹, and 4095 cm⁻¹ with PBE, PBE0, and B3LYP, respectively, along with a calculated anharmonic infrared peak at 4146 cm⁻¹. These calculated characteristic peaks closely match those observed in “amber centers” (4065 cm⁻¹ and 4165 cm⁻¹). However, based on the additional simulated anharmonic infrared peak at 3792 cm⁻¹, NVH₄⁺ cannot be assigned to the 4165 cm⁻¹ band. It is possible to assign the 4065 cm⁻¹ band to NVH₄⁺; even though it can remain stable in diamond at 1973 K, establishing and measuring this benchmark could be challenging. Although NVH₄⁺ is uncertain as a structure in “amber centers”, a model of the N–H bond under repulsion stretching is proposed, which can generate a vibrational frequency surpassing 4000 cm⁻¹. It may provide a useful avenue for investigating high wavenumber defect structures in diamond.