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It is possible to construct various other defect structures that act
as double donors, involving different numbers of oxygen atoms
(O_{ni}, ). We have also modelled many of these for
comparison with the diylid model, and to determine whether they
could be responsible for other members of the thermal donor family.
Figure 9.10:
The top KohnSham eigenvalues for various alternative thermal
donor models, all in the +2 charge state. Black boxes denote filled
state, white boxes for empty states. The eigenvalues have been
arbitrarily scaled to the experimental band gap of 1.16eV. Structures
are 3O_{i} species (a) Snyder/Stavola, (b) Partially dissociated
trimer, 4O_{i} species (c) `Flanked square' model, (d) Disquare
model, (e) 5O_{i} STD analogue, and (f) 6O_{i} diylid with dimer in
central SiSi backbonds.

Chris Ewels
11/13/1997