Specifying vacancies

Suppose if we want to know the defect formation energy of a single nitrogen vacancy, when I specify "vacancy N " in GULP. The output says only one defect has been created.
But how can I take it confidently that only one nitrogen vacancy is being created ?

I want to study the defect formation energy in the presence of one vacancy only. How can I know that specifying as “vacancy N” for say, calcium nitride ensures only one nitrogen vacancy is created though the output says 1 defect has been created ?

Computer software doesn’t generally play pranks on you, so if it says that one vacancy has been created then usually that’s what it’s done. :slight_smile:
You could be more specific and give the coordinates of the vacancy you want in the input. You could also count the number of atoms in the non-defective region 1 and the defective region 1 to see that they differ by 1, or take the coordinates from the output and visualise them to look for the vacancy.