AB-INITIO CALCULATIONS OF THE ENERGETICS OF THE NEUTRAL SI VACANCY DEFECT

Ab initio plane-wave pseudopotential calculations for the neutral sili con vacancy indicate a formation energy of 3.6 eV, with the surroundin g lattice undergoing a tetragonal distortion with the nearby atoms for ming two dimers having bond lengths 2.91 Angstrom. Close in energy is a tetrahedrally distorted structure in which the nearby atoms relax to wards the vacancy by 12.6% of the bulk bond length. Additional distort ions with trigonal symmetry were also investigated, but no stable stru ctures were found. The symmetry, energetics, and geometry are found to be a sensitive function of the computational basis-set and supercell used in the plane-wave calculations.