The ABINIT Users Mailing List ( CLOSED )

["Allan, Douglas C Dr" <AllanDC@Corning.com>]

Another and perhaps better way to select compatible k-points is to start with 
a single k-point in the supercell (since it is a supercell a grid of multiple 
k-points does not really make sense) and then do zone-folding to make a set 
of k-points in the primitive cell.  In the absence of the vacancy in the 
supercell this should produce the same energy/atom in both cases to very good 
accuracy; they results should agree within the tolerance you supply for 
convergence.  Then when you put the vacancy in the supercell you can better 
trust the energy comparisons between the two cells.

-----Original Message-----
From: Steven Homolya [mailto:Steven.Homolya@spme.monash.edu.au] 
Sent: Wednesday, October 08, 2003 11:01 PM
To: forum@abinit.org
Subject: Re: [abinit-forum] Vacancy-formation energy with abinit


On Thu, 9 Oct 2003 12:26 am, homegchiche@yahoo.fr wrote:
> I have another question about the study of vacancy with abinit. I 
> would like to know if the present code could give directly self 
> consistent Vacancy-formation energy.
>

Not sure what you mean by directly.

The most direct way I know is to first do a calculation for the pure 
substance. This is a small calcn., since you just use the primitive unit 
cell, usually one atom per cell. This gives total energy per atom, say 
E_pure. Then do a supercell calculation with N>>10 sites, where one atom has 
been removed. This gives energy, say E_scell, for the N-1 atom supercell. 
Then the energy of formation of the vacancy is

E_scell - (N-1)*E_pure

Make sure the two calculations use compatible parameters. In particular, 
number of k-points should be proportional to volume of reciprocal unit cell 
(inversely prop. to volume of supercell). You can try atuto generating k-mesh 
keeping kptrlen the same for the two calcns. (though I found that this fails 
someimes, may be a bug?)

-- 
Steven Homolya
School of Physics and Materials Engineering
Monash University VIC 3800
Australia
Tel: INT +61 3 9905 3694
Fax: INT +61 3 9905 3637