Looking for $$sp^2$$ s p 2 carbon atoms in diamond: a quantum mechanical study of interacting vacancies

Abstract

This paper reports the calculated relaxed lattice configurations and corresponding electronic and magnetic structures, and Raman frequencies of two divacancies in diamond, V2 and VC=CV, in which the vacancies are first and third neighbours respectively. The calculations are formulated within a supercell approach to local defects in crystalline solids, here 64-and 128-atoms unit cells and based largely on the B3LYP one-electron approximation constructed from an all-electron Gaussian basis set. Three important findings are first, that, of the four possible spin states, Sz=0, 1, 2, 3, the singlet is predicted to be lowest in energy for both divacancies; second, that the singlet state of V2 is ∼1.7 eV lower in energy than that in VC=CV; and third, that the Raman peak at 1628 cm −1 in defective diamond can be ascribed to the presence of a C=C double bond, as in the singlet state of VC=CV.

Probing the Nanostructure of Neutron-Irradiated Diamond Using Raman Spectroscopy

“…Different tentative attributions have been formulated for the 1430 (1450) and 1480 (1501) cm −1 peaks [14], involving vacancy [41,65], intrinsic/nitrogen interstitial defects [67,68], or a vacancy or a divacancy surrounded by conjugated single and double carbon-carbon bonds (the R4/W6 center) [21,69]. Recent calculations [70] based on the B3LYP hybrid implementation of density functional theory [71] show the absence of peaks in the region of 1490 cm −1 in the spectra of both divacancy V 2 and V-C=C-V. According to Reference [72], the calculated Raman-active high-frequency local vibrational modes of di-interstitials (1461, 1495, 1813, and 1826 cm −1 ) agree well with the bands often observed in the Raman spectra of radiation-damaged diamonds.…”