<div dir="ltr">Differences between DFT lattice parameters and experiment are well known, although smaller (as you have) is less common. (Maybe because you did not use +U).<div><br></div><div>For "better" results, there are many methods one common being PBEsol. There is a large literature on this. Of course, whether this is really better is less clear -- why should the lattice parameters at T=0K be the same as experiment, and how clean is the sample in experiment?</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jul 25, 2017 at 5:49 AM, Chouaib AHMANI FERDI <span dir="ltr"><<a href="mailto:ahmaniferdichouaib@gmail.com" target="_blank">ahmaniferdichouaib@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<div dir="ltr">
<div class="gmail_default" style="font-family:georgia,serif">Thank you for your response.</div>
<div class="gmail_default" style="font-family:georgia,serif"><br>
</div>
<div class="gmail_default" style="font-family:georgia,serif">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.</div>
<div class="gmail_default" style="font-family:georgia,serif"><br>
</div>
<div class="gmail_default" style="font-family:georgia,serif">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.</div>
<div class="gmail_default" style="font-family:georgia,serif"><br>
</div>
<div class="gmail_default" style="font-family:georgia,serif">Exp : a = 8.4599 A and u = 0.2563</div>
<div class="gmail_default" style="font-family:georgia,serif">optimized : a = 8.2713 A and u = 0.2642 (more distortion of tetrahedra and octahedra)</div>
<div class="gmail_default" style="font-family:georgia,serif"><br>
</div>
<div class="gmail_default" style="font-family:georgia,serif">(GGA-PBE), rkm = 6.5, k-points = 40</div>
<div class="gmail_default" style="font-family:georgia,serif"><br>
</div>
<div class="gmail_default" style="font-family:georgia,serif">Is there any method that could yield better results ?</div>
<div class="gmail_default" style="font-family:georgia,serif"><br>
</div>
<div class="gmail_default" style="font-family:georgia,serif">Faithfully,</div>
<div class="gmail_default" style="font-family:georgia,serif"><br>
</div>
<div class="gmail_default" style="font-family:georgia,serif"><br>
</div>
<div class="gmail_default" style="font-family:georgia,serif"> </div>
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<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Jul 24, 2017 at 2:09 PM, Fecher, Gerhard <span dir="ltr">
<<a href="mailto:fecher@uni-mainz.de" target="_blank">fecher@uni-mainz.de</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I would first check if the structure was realy completely solved in previous work.<br>
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.<br>
If one uses these parameters (and they do not accidentially fit the real ones) then the electronic structure will be most probably not correct,<br>
this concerns also all other parameters (e.g. magnetic moments, optical spectra, etc.)<br>
Indeed you do not need to optimize positions if they are fixed by symmetry.<br>
<br>
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.<br>
In some cases you may find afterwards that the structure initially thought about might be wrong.<br>
<br>
Ciao<br>
Gerhard<br>
<br>
DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:<br>
"I think the problem, to be quite honest with you,<br>
is that you have never actually known what the question is."<br>
<br>
==============================<wbr>======<br>
Dr. Gerhard H. Fecher<br>
Institut of Inorganic and Analytical Chemistry<br>
Johannes Gutenberg - University<br>
55099 Mainz<br>
and<br>
Max Planck Institute for Chemical Physics of Solids<br>
01187 Dresden<br>
______________________________<wbr>__________<br>
Von: Wien [<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at" target="_blank">wien-bounces@zeus.theochem.tu<wbr>wien.ac.at</a>] im Auftrag von
<a href="mailto:tran@theochem.tuwien.ac.at" target="_blank">tran@theochem.tuwien.ac.at</a> [<a href="mailto:tran@theochem.tuwien.ac.at" target="_blank">tran@theochem.tuwien.ac.at</a>]<br>
Gesendet: Montag, 24. Juli 2017 14:47<br>
An: A Mailing list for WIEN2k users<br>
Betreff: Re: [Wien] experimental vs relaxed parameters using wien2k<br>
<div>
<div class="m_-775321396452603143h5"><br>
Hi,<br>
<br>
If you are not interested in structural properties because<br>
this is not the topic of the paper you want to write, then just use<br>
the available experimental structure for band structure, optics, etc.<br>
<br>
When no experimental structure is available, then you have no choice<br>
but the problem is to choose the appropriate functional to calculate<br>
the structure.<br>
<br>
FT<br>
<br>
On Monday 2017-07-24 14:27, Chouaib AHMANI FERDI wrote:<br>
<br>
>Date: Mon, 24 Jul 2017 14:27:43<br>
>From: Chouaib AHMANI FERDI <<a href="mailto:ahmaniferdichouaib@gmail.com" target="_blank">ahmaniferdichouaib@gmail.com</a>><br>
>Reply-To: A Mailing list for WIEN2k users <<a href="mailto:wien@zeus.theochem.tuwien.ac.at" target="_blank">wien@zeus.theochem.tuwien.ac.<wbr>at</a>><br>
>To: <a href="mailto:wien@zeus.theochem.tuwien.ac.at" target="_blank">wien@zeus.theochem.tuwien.ac.a<wbr>t</a><br>
>Subject: [Wien] experimental vs relaxed parameters using wien2k<br>
><br>
>Greatings Wien users,<br>
><br>
>I just want to ask if the experimental parameters (lattice parameters,<br>
>internal parameter, atomic positions, ...) are already available for a<br>
>certain compound, would it be better to run SCF cycle with them or to make<br>
>preliminary relaxation and volume optimization and then perform SCF cycle<br>
>using the calculated parameters.<br>
><br>
>Faithfully,<br>
><br>
> <br>
><br>
>--<br>
>AHMANI FERDI Chouaïb<br>
>Ph.D Student in Material Science<br>
>Ecole Normale Supérieure<br>
>Mohammed V University, Rabat.<br>
>Tel : +212 6 94 59 57 60<br>
><br>
><br>
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><br>
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<div dir="ltr"><font face="georgia, serif">AHMANI FERDI Chouaïb</font></div>
<div dir="ltr"><font face="georgia, serif">Ph.D Student in Material Science </font></div>
<div dir="ltr"><font face="georgia, serif">Ecole Normale Supérieure</font></div>
<div dir="ltr"><font face="georgia, serif">Mohammed V University, </font><span style="font-family:georgia,serif;font-size:12.8px">Rabat. </span></div>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><span style="font-size:12.8px">Professor Laurence Marks</span><br></div><div dir="ltr"><span style="font-size:12.8px">"Research is to see what everybody else has seen, and to think what nobody else has thought", </span><span style="font-size:12.8px">Albert Szent-Gyorgi</span><br><a href="http://www.numis.northwestern.edu" target="_blank">www.numis.northwestern.edu</a> ; <span style="font-size:12.8px">Corrosion in 4D: </span><a href="http://MURI4D.numis.northwestern.edu" style="font-size:12.8px" target="_blank">MURI4D.numis.northwestern.edu</a><div><span style="font-size:12.8px">Partner of the CFW 100% program for gender equity, </span><a href="http://www.cfw.org/100-percent" style="font-size:12.8px" target="_blank">www.cfw.org/100-percent</a></div><div>Co-Editor, Acta Cryst A</div></div></div></div></div></div></div></div></div></div></div>
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