Looking for sp2carbon atoms in diamond: a quantum mechanical study of interacting vacancies

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-atom 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. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.