The neutral vacancy in silicon and diamond: Generalized valence bond studies

Self-consistent ab initio generalized valence bond and configuration interaction calculations are presented for molecular cluster models of the electronic states of the neutral vacancy in diamond and silicon. In each case the ground state of the vacancy is found to be ¹E (T_d designation) with the ³T₁ and ⁵A₂ states slightly higher (0.18 eV and 0.60 eV for Si and 0.33 eV and 1.2 eV for C). The first excited singlest state is ¹T₂ in each case. The ¹E-¹T₂ excitation energy is foundto be 1.7 ± 0.7 eV for diamond and 1.3 ± 0.5 eV in silicon, the range being due to uncertainty in the model used for estimating the polarization effects due to the remainder of the infinite crystal.