Bader charges bulk vs supercell

[arwa68]

Dear Mr,
I am using Bader charges to calculate charge difference. However, the bulk values seems to be always larger than that in the supercell. I do have interface with other material in my supercell, but even in the bulk-like region it is larger. Also, I can see from the DOS that there is charge gain in some region(CB shift to lower energy and cross Fermi energy), but since the value is large the substraction shows missing charge instead of gain.
Is there any specific reason that makes the charge in the supercell differnt from the unit-cell?

Thanks