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

摘要

Quantum-mechanical ab initio calculations are performed to elucidate thevibrational spectroscopic features of a common irradiation-induced defect indiamond, i.e. the neutral vacancy. Raman spectra are computed analyticallythrough a Coupled-Perturbed-Hartree-Fock/Kohn-Sham approach as a function ofboth different defect spin states and defect concentration. The experimentalRaman features of defective diamond located in the 400-1300 cm-1 spectralrange, i.e. below the first-order line of pristine diamond at 1332 cm-1 , arewell reproduced, thus corroborating the picture according to which, at lowdamage densities, this spectral region is mostly affected by non-graphitic sp3defects. No peaks above 1332 cm-1 are found, thus ruling out previous tentativeassignments of different spectral features (at 1450 and 1490 cm-1) to theneutral vacancy. The perturbation introduced by the vacancy to the thermalnuclear motion of carbon atoms in the defective lattice is discussed in termsof atomic anisotropic displacement parameters (ADPs), computed from convergedlattice dynamics calculations.