[Wien] Bad formation energies for the charged vacancies

[Peter Blaha]

> Is the question regarding the computation of total energy per unit  cell 
> in an infinite crystal with non-neutral unit cells? If so, then  the 
> total energy diverges -- and so is not well-defined. (So  neutralizing 
> backgrounds must be added in such cases to obtain  meaningful results, 
> etc.)

Yes, this is the question and yes, of course we add a positive or negative background.
We are quite confident that the resulting potential is ok, but the question is if there
is a correction to the total energy due to the background charge.
I believe: yes (something like Q * V-col_average / 2), but my problem is that V-coul
is in an infinite crystal only known up to an arbitrary constant and thus this correction
is "arbitrary".

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Peter Blaha
Inst. Materials Chemistry, TU Vienna
Getreidemarkt 9, A-1060 Vienna, Austria
Tel: +43-1-5880115671
Fax: +43-1-5880115698
email: pblaha at theochem.tuwien.ac.at
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