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[<rolando.saniz@ua.ac.be>]

Dear Matthieu,

Thanks for your reply. It has clarified a lot to us.

Regarding the total energy in the case of charged impurities, however, our
question was not really refering to supercell size corrections. We are not 
sure
of what is done in Abinit in the following sense. It appears that total energy
calculations in most codes are done using the total energy expression of Ihm,
Zunger, and Cohen [J. Phys. C 12, 4409 (1979)]. But this expression is valid
only for charge-neutral systems [see, e.g., Lany and Zunger, PRB 78, 235104
(2008)]. If the same total energy expression is used for charged supercells,
then the total energy will be defined only up to a constant. So the question
would be, is a compensating background added in Abinit for charge neutrality,
or is the total energy expression used adapted to charged supercell cases,
i.e., is the total energy free of an arbitrary reference?

Thanks for your time!

Best regards,
Rolando

**********
Rolando Saniz
Departement Fysica
Universiteit Antwerpen