[Wien] experimental vs relaxed parameters using wien2k

[Chouaib AHMANI FERDI]

Thank you for your response.

If experimental data is available, I believe from what it has been said it
is better to use them, otherwise, one have to perform optimization.

I did one myself on ZnFe2O4 and found a value of the cubic lattice
parameter "a" not so close to experiment. also the internal parameter was
not that near.

Exp :               a = 8.4599 A and u = 0.2563
optimized :    a = 8.2713 A and u = 0.2642     (more distortion of
tetrahedra and octahedra)

(GGA-PBE), rkm = 6.5, k-points = 40

Is there any method that could yield better results ?

Faithfully,




On Mon, Jul 24, 2017 at 2:09 PM, Fecher, Gerhard <fecher at uni-mainz.de>
wrote:

> I would first check if the structure was realy completely solved in
> previous work.
> I found that e.g. in the Pearson's crystal data base the structural
> parameters (atomic positions) for the prototype are reported for many
> compounds.
> If one uses these parameters (and they do not accidentially fit the real
> ones) then the electronic structure will be most probably not correct,
> this concerns also all other parameters (e.g. magnetic moments, optical
> spectra, etc.)
> Indeed you do not need to optimize positions if they are fixed by symmetry.
>
> Therefore my advice is, if the structure was not determined by yourself
> (or in your group) you should optimize it first before thinking about the
> calculated properties.
> In some cases you may find afterwards that the structure initially thought
> about might be wrong.
>
> Ciao
> Gerhard
>
> DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
> "I think the problem, to be quite honest with you,
> is that you have never actually known what the question is."
>
> ====================================
> Dr. Gerhard H. Fecher
> Institut of Inorganic and Analytical Chemistry
> Johannes Gutenberg - University
> 55099 Mainz
> and
> Max Planck Institute for Chemical Physics of Solids
> 01187 Dresden
> ________________________________________
> Von: Wien [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von
> tran at theochem.tuwien.ac.at [tran at theochem.tuwien.ac.at]
> Gesendet: Montag, 24. Juli 2017 14:47
> An: A Mailing list for WIEN2k users
> Betreff: Re: [Wien] experimental vs relaxed parameters using wien2k
>
> Hi,
>
> If you are not interested in structural properties because
> this is not the topic of the paper you want to write, then just use
> the available experimental structure for band structure, optics, etc.
>
> When no experimental structure is available, then you have no choice
> but the problem is to choose the appropriate functional to calculate
> the structure.
>
> FT
>
> On Monday 2017-07-24 14:27, Chouaib AHMANI FERDI wrote:
>
> >Date: Mon, 24 Jul 2017 14:27:43
> >From: Chouaib AHMANI FERDI <ahmaniferdichouaib at gmail.com>
> >Reply-To: A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.
> at>
> >To: wien at zeus.theochem.tuwien.ac.at
> >Subject: [Wien] experimental vs relaxed parameters using wien2k
> >
> >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
> >
> >
> >[signature.gif?u=139409&e=8673185&v=632ab2fe5f7587109472ad46fdedd2
> b235e7342
> >ab64c99b4930f7b42d8fd3fb2]
> >
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-- 
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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