Raman spectroscopic features of the neutral vacancy in diamond from ab initio quantum-mechanical calculations

TL;DR

This study uses ab initio quantum-mechanical calculations to analyze the Raman spectroscopic features of the neutral vacancy in diamond, successfully matching experimental data and clarifying spectral feature assignments.

Contribution

It provides a detailed theoretical analysis of the neutral vacancy's vibrational features in diamond, clarifying previous spectral feature assignments and demonstrating the effectiveness of ab initio methods.

Findings

Reproduces experimental Raman spectra of defective diamond.

Rules out previous spectral feature assignments at 1450 and 1490 cm-1.

Shows the defect's impact on atomic displacement parameters.

Abstract

Quantum-mechanical ab initio calculations are performed to elucidate the vibrational spectroscopic features of a common irradiation-induced defect in diamond, i.e. the neutral vacancy. Raman spectra are computed analytically through a Coupled-Perturbed-Hartree-Fock/Kohn-Sham approach as a function of both different defect spin states and defect concentration. The experimental Raman features of defective diamond located in the 400-1300 cm-1 spectral range, i.e. below the first-order line of pristine diamond at 1332 cm-1 , are well reproduced, thus corroborating the picture according to which, at low damage densities, this spectral region is mostly affected by non-graphitic sp3 defects. No peaks above 1332 cm-1 are found, thus ruling out previous tentative assignments of different spectral features (at 1450 and 1490 cm-1) to the neutral vacancy. The perturbation introduced by the vacancy to the thermal nuclear motion of carbon atoms in the defective lattice is discussed in terms of atomic anisotropic displacement parameters (ADPs), computed from converged lattice dynamics calculations.