[Pw_forum] Site Occupancy

Eyvaz Isaev eyvaz_isaev at yahoo.com
Wed Aug 20 12:19:04 CEST 2008

Dear Ahmet,

Pseudopotential and most of Full-Potential programs can not deal with fractional site occupation.
The only way for this purpose is the use of programs within Coherent-Potential-Approximation.
But, actually, I am not sure it will work in your case, as you have to mix "empty sphere" and H to get fully occupied site.

If you ("randomly") remove some H atoms you will get correct stoichiometry, though each H site is fully occupied.

Please also provide your affiliation.


Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com

--- On Wed, 8/20/08, Ahmet Cicek <acicek at akdeniz.edu.tr> wrote:

> From: Ahmet Cicek <acicek at akdeniz.edu.tr>
> Subject: [Pw_forum]  Site Occupancy
> To: "PWSCF Forum" <pw_forum at pwscf.org>
> Date: Wednesday, August 20, 2008, 12:22 PM
> ---------- Forwarded message ----------
> From: Ahmet Cicek <islicam at gmail.com>
> Date: Wed, Aug 20, 2008 at 11:21 AM
> Subject: [Pw_forum] Site Occupancy
> To: PWSCF Forum <pw_forum at pwscf.org>
> Hi,
> I am trying to obtain the band structure of Ammonium
> Hexafluorosilicate-(NH_4)_2SiF_6-where the space group is
> Fm3m, location and
> occupancies* of the base atoms are:
> atom           position                        occupancy
> ------------------------------------------------------------------------
> Si               (0,0,0)                             1
> F                (0.2011,0,0)                     1
> N                (0.25,0.25,0.25)               1
> H                (0.168,0.168,0.269)          1/3
> When the structure is contructed via symmetry operations,
> the number of the
> H atoms are three times the actual value. Could you please
> help me in how to
> use the knowledge of "occupancy" of the H atoms
> so that the band structure
> calculation gives results corresponding to the physical
> structure?
> Thank you.
> *http://rruff.geo.arizona.edu/AMS/result.php?mineral=cryptohalite
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