Thank you Marcos.  I will search for "ghost atom" in the manual rather then 
"vacancy" to see what keywords I need.

Cheers
Bill


On 4/21/10 1:56 PM, "Marcos Veríssimo Alves" <[email protected]> 
wrote:

I'd say you'd only need ghost atoms (the basis functions you talk about) if you 
need to calculate the formation energy of the vacancy - the so-called BSSE 
correction.

Marcos

On Wed, Apr 21, 2010 at 7:49 PM, Shelton Jr, William Allison 
<[email protected]> wrote:
I might be mistaken but doesn't siesta use atom-centered basis ?  If so, don't 
you need to put some basis functions on the vacant site ?

Cheers
Bill


On 4/21/10 1:39 PM, "Marcos Veríssimo Alves" <[email protected]> 
wrote:

Just as a vacancy in real life, a vacancy in a DFT calculation is not an 
addition, but a removal... :)

All you need to do is to remove the undesirable atom(s) from the atom 
coordinates list in your supercell. Of course, don't forget to update the 
number of atoms.

Marcos

On Wed, Apr 21, 2010 at 7:30 PM, Shelton Jr, William Allison 
<[email protected]> wrote:
Can siesta treat vacancies ?  If so, how can it be added to the input file ?

Cheers
Bill




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