Large Pairing Jahn-Teller Distortions Around Divacancies in Crystalline Silicon

Ab initio atomic and electronic structures of neutral $\left(V_2^0\right)$ and charged $\left(V_2^{+}{,V}_2^{-}{,V}_2^{2-}\right)$ Si divacancies are investigated using bulk-terminated clusters with up to $\approx 320$ Si atoms. For the first time, the relaxed structures for $V_2^{+}$, $V_2^0$, and $V_2^{-}$ are found to exhibit large pairing Jahn-Teller distortions consistent with electron paramagnetic resonance experiments. Atomic relaxations, Jahn-Teller and relaxation energies, and hyperfine parameters are calculated for various charge states and compared with available experimental data. The cluster size and the anisotropic nature of the relaxations play key roles in establishing the stability of the structures with large pairing distortions.