# Calculation of defect in bulk of a wafer model

I’d like to estimate defect in bulk of a model. When cheking literatures, typical SiO2 has something like defect density of 5x10^17 cm^-3. Is it possible to perform similar calculation using ASE SiO2 model? I could not find similar topic, so I’d like to get some hints from this community. thank you in advance.

In addition, is it possible to calculate void/vacancy of a model?

I’m afraid this question is not specific enough.

cubic cm per defect = 1/(5e17) = 2e-18
cubic Angstrom per cubic cm = 10^(10-2) = 1e24
cubic Angstrom per defect = 1e24 * 2e-18 = 2e6

Volume of quartz unit cell (9 atoms) = 109 cubic Angstrom

Atoms per supercell containing one defect: 9 * 2e6 / 109 = 165138

You will need quite an efficient calculator to perform such a calculation. I don’t know what “ASE SiO2 model” is; if you can be clearer about that then maybe the question can be answered.

I’m not sure that any method currently feasible for so many atoms will also handle the electronic localisation correctly for accurate defect energies. The good news is that defect calculations are typically performed at rather exaggerated concentrations in order to make them computationally tractable. The results can be extrapolated to lower concentrations if necessary.