[Wien] experimental vs relaxed parameters using wien2k

[Fecher, Gerhard]

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=632ab2fe5f7587109472ad46fdedd2b235e7342
>ab64c99b4930f7b42d8fd3fb2]
>