[Wien] Convergence problem in mbj potential calculation

[shamik chakrabarti]

Dear Pieper & Laurence,

                         Thank you for your valuable suggestions. I would
try to follow your advises and come up with a feasible solution.
Thanks once again.

with kind regards,




On Thu, Jun 15, 2017 at 4:33 PM, Laurence Marks <L-marks at northwestern.edu>
wrote:

> To add one small thing; you can remove all the Li and it will still
> "match" the XRD. If it is powder data, you can probably remove all the O
> and it will still "match".
>
> ---
> Professor Laurence Marks
> "Research is to see what everybody else has seen, and to think what nobody
> else has thought", Albert Szent-Gyorgi
> http://www.numis.northwestern.edu
> Corrosion in 4D http://MURI4D.numis.northwestern.edu
> Partner of the CFW 100% gender equity project, www.cfw.org/100-percent
> Co-Editor, Acta Cryst A
>
>
> On Jun 15, 2017 05:52, "pieper" <pieper at ifp.tuwien.ac.at> wrote:
>
> You keep getting back to this match between the (presumably powder-)xrd
> you calculated from your .struct file and the experimental one. This
> does NOT imply that your structural model describes the physical
> situation correctly! With your - in Gerhards words - 'interesting
> approach' you should be able to produce any number of different .struct
> files, and calculating their powder-xrd find a similar 'match with the
> experimental one'.
>
> Did you calculate the xrd with any of the alternative distributions of
> Li, Ni and Ti on their sites in your unit cell? Did you try the same
> with the many, many other distributions you can generate in larger
> supercells? I am prettty sure you will find something that matches your
> xrd data. It will make as much sense as what you have now ...
>
> Be aware of the fact that structural models of Wien2k have symmetry
> properties  different from your physical situation: in your model the
> metal atoms occupy lattice sites regularly, breaking certain symmetries
> of the underlying lattice. The actual distribution in your case is
> (apparently more or less) random, which overall breaks no symmetry, but
> locally breaks every symmetry somewhere.
>
> If the distribution of Li, Ni, and Ti  really is random on one shared
> site I know of only one (expensive) way to proceed: try to reduce the
> influence of short range periodicity in your models by increasing the
> size of the supercell and putting Li, Ni, and Ti at random positions. Do
> structural relaxations, look what changes in your (GGA-) calculations,
> and keep fingers crossed that things you are interested in converge for
> supercells of a size you still can handle.
>
>
>
> ---
> Dr. Martin Pieper
> Karl-Franzens University
> Institute of Physics
> Universitätsplatz 5
> A-8010 Graz
> Austria
> Tel.: +43-(0)316-380-8564
>
>
>
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>


-- 
Dr. Shamik Chakrabarti
Post Doctoral Research Associate
Dept. of Condensed Matter Physics and  Material Science
S N Bose National Centre for Basic Sciences
Kolkata-700098
INDIA
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