Here, <110> vacancy chains, multi-vacancy clusters and vacancy discs were modeled using density functional theory within the AIMPRO and DFTB codes. While a connection could be established between the results on vacancy chains and previous electron paramagnetic resonance experiments, no connection could be made between the point defects and the optical properties of natural type-IIa brown diamonds. However, a vacancy disc consisting of a {111} double plane of vacancies was stable and possessed an absorption spectrum similar to that found in brown diamonds.

Optical Properties of Vacancy Related Defects in Diamond. L.S.Hounsome, R.Jones, P.M.Martineau, M.J.Shaw, P.R.Briddon, S.Öberg, A.T.Blumenau, N.Fujita: Physica Status Solidi A, 2005, 202[11], 2182-7