Embedding methods which had been developed for treating large molecules with bulky ligands, or in polar solvents, were used to describe the electronic structures of point defects in covalently bonded SiO2, Si3N4 and Si2N2O. The relaxation of the lattice around a given defect, especially an anion vacancy or an interstitial, was described by using an approach in which the system was partitioned into 2 regions: with the local defect treated at the gradient-corrected level, and the surrounding matrix treated by using a semi-empirical Hamiltonian. In this way, clusters of 100 atoms or more could be used to describe a portion of the solid which was 1 to 1.5nm in diameter. The long-range lattice polarization which was produced by a charged defect, a charged O vacancy or a proton bound to O or N atoms, was estimated by using the iso-density polarized continuum model. The 2 embedding schemes provided a simple means for improving cluster models for neutral and charged defects in covalent materials.

Simplified Embedding Schemes for the Quantum-Chemical Description of Neutral and Charged Point Defects in SiO2 and Related Dielectrics. D.Erbetta, D.Ricci, G.Pacchioni: Journal of Chemical Physics, 2000, 113[23], 10744-52