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Six oxygen atom TD species

It is possible to insert an additional dimer into the di-y-lid structure, with one oxygen atom in each of the Si-Si bonds below the core Si atom. This pushes the core Si atom upwards into the defect until the trivalent oxygen atoms are closer to this core atom than their outer Si neighbours. We relaxed such a defect in the 148 atom cluster used above, but the defect is then really too large for such a cluster and more bulk Si material is needed to accurately simulate the surrounding lattice relaxation, which is extensive. However the defect core maintains its shallow double donor nature (see Figure 9.10f) and the structure does not spontaneously relax into any other; thus it remains a possible candidate for the next in the TD series.

Chris Ewels