[Wien] How to use wien2k to calculate defect formation energy?

[yxl at email.jlu.edu.cn]

Dear users,
     In WIEN2k-FAQ, it said 
 it is usually NOT possible just to double the cells and leave all atoms at their ideal and equivalent positions. This would lead to large multiplicities (e.g. in big supercells even more than 48 atoms could be "equivalent" and of course there is NO SPACEGROUP corresponding to this type of cell, since they all can be reduced by translation symmetry.
 But when we want to calculate the defect formation energy ,we need to calculate the nenergy of defect-free system.
So how to calculate the defect formation energy with wien2k?
Thanks in advance!
yours sincerely,
hongxia