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.