[Wien] Formation energy of a deffective lattice

[Stefaan Cottenier]

This reminds me to a related issue on which I never found a satisfying 
answer. Perhaps someone has ideas or references? The equation given by 
Ricardo Faccio applies to a defect that is created by a previously 
isolated atom that gets incorporated into the bulk and stays there. But 
what if you want to *compare* the formation energy of such a case with 
the formation energy of a case where the previously isolated atom 
*replaces* a bulk atom? The best I can think about is to add a dummy 
isolated bulk atom in the equation, to have the same number of atoms at 
either side of the minus sign:

E(defect_formation)=[E(defective)+E(isolated bulk atom)] - 
[E(bulk)+E(isolated_impurity_atom)]

But I'm not sure this is really correct. For instance, can this be 
related in some way to the chemical potential? I bet many people have 
thought about this before. If anyone has recipes or references, I'm 
interested to hear them.

Stefaan


Peter Blaha wrote:

>http://www.wien2k.at/reg_user/faq/cohesive.html
>
>Ricardo Faccio schrieb:
>  
>
>>Hi 
>>
>>    I'm performing calculations for defective supercells.  
>>
>>The formation energy for a system could be=  
>>
>>E(defect_formation)=E(defective)-[E(bulk)+E(isolated_atom)].  
>>
>>    My problem is related with the total energy for an isolated atom, 
>>Wien take as a reference the average potential of the supercell, but how 
>>to deal with it in the case of a single atom. So, how can I perform a 
>>calculation for an isolated atom in order to be considered in the 
>>previous formula? 
>>    
>>
>
>
>                                       P.Blaha
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