[Wien] Bad formation energies for the charged vacancies

[John Pask]

Dear Peter,

Yes, the background charge must be taken into account as part of the  
net-neutral total charge in order to have well-defined total energy.  
Then as long as the compensation charge is then in exactly the same  
way as the remaining "physical" charge (i.e., enters all the same  
integrals), then the arbitrary constant in potential should not matter  
since:

\int{ \rho (V + c)}  = \int{ \rho V}  + c \int{ \rho} = \int {\rho V},

independent of arbitrary constant c.

John

On Feb 24, 2010, at 11:54 PM, Peter Blaha wrote:

>> 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".
>
> -- 
> -----------------------------------------
> 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
> -----------------------------------------
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://*zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>