  We perform total energy calculations based on the tight-binding Hamiltonian
scheme (i) to study the structural properties and energetics of the extended
{311} defects depending upon their dimensions and interstitial concentrations
and (ii) to find possible mechanisms of interstitial capture by and release
from the {311} defects. The generalized orbital-based linear-scaling method
implemented on Cray-T3D is used for supercell calculations of large scale
systems containing more than 1000 Si atoms.
