[Wien] experimental vs relaxed parameters using wien2k

[Chouaib AHMANI FERDI]

​Dear Wien2k users,​

Thank you for your feedback.

If I got this right, I see that the optimization doesn't lead necessary to
a good results and experimental data are there to evaluate the accuracy of
the calculation method, and by that I mean the choice of parameters,
potential, structure ...
The methodology depends also on the purpose of the calculation, and the
properties we are looking for.

However, given the large interval in which reside the lattice parameters
provided by different papers, how to be quite sure we have chosen the
correct structure or that is closest to reality. I am aware of the fact
that this is a vague question given the variety of the different compounds
but is there at least some indications visible before or after the SCF
cycles that could help evaluate the credibility of the .struct file ?

Faithfully,



On Tue, Jul 25, 2017 at 4:55 PM, Tristan de Boer <tristan.deboer at usask.ca>
wrote:

> You can find many papers that use either approach. I considered this
> somewhat tangentially in a paper on several semiconductor polymorphs that
> were synthesized under different pressures. [1] We collected x-ray
> absorption and emission spectra on thee polymorphs, and compared our
> spectra to those calculated using the PBE GGA functional for both relaxed
> and unrelaxed atom positions. We found that there was worse agreement with
> experiment using relaxed parameters compared to the experimental
> parameters, so at least for this case, using the experimental structure
> yields more correct results. I'm not sure how universal this is, and it may
> not apply as you move higher up the 'Jacob's ladder' of density functional
> approximations.
> Best Regards,
> Tristan
>
> [1] doi:10.1103/PhysRevB.93.155205
>
>
> On 2017-07-24 6:27 AM, Chouaib AHMANI FERDI wrote:
>
>> Greatings Wien users,
>>
>> I just want to ask if the experimental parameters (lattice parameters,
>> internal parameter, atomic positions, ...) are already available for a
>> certain compound, would it be better to run SCF cycle with them or to
>> make preliminary relaxation and volume optimization and then perform SCF
>> cycle using the calculated parameters.
>>
>> Faithfully,
>>
>>
>>
>> --
>> AHMANI FERDI Chouaïb
>> Ph.D Student in Material Science
>> Ecole Normale Supérieure
>> Mohammed V University, Rabat.
>> Tel : +212 6 94 59 57 60
>>
>>
>>
>>
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-- 
AHMANI FERDI Chouaïb
"Laboratoire Matériaux Nanomatériaux Nanomagnétisme
  et Enseignement des Sciences"
Ecole Normale Supérieure
Université Mohammed V, Rabat.
Tel : +212 6 94 59 57 60
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