[Wien] Can I get some example for crystal defect?

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Dear All

I plan to make a defective crystal model.
For example, in TaN crystal I want to put substitutial or institutial Oxygen atom and to calculate its DOS. 

I think that a supercell should be made, next the stable Oxygen position should be found and then its DOS could be calculated. But I'm not sure this method is wright. 

If you have a proper example, could I share it?

my best

mino korea.