[Wien] Relaxation of already known structure

[Jihoon Park]

Dear All,

Thank you for your replied all. It helps me a lot.
I usually only calculate magnetic properties, and it seems like that the
relaxation does not affect the magnetic properties much (at least the
material I calculate now).
I am wondering if the other properties are affected a lot more. Because two
of my coworkers in another university told me that the relaxation must be
performed for all calculations.
I am still not sure how to convince myself.
If the magnetic properties for relaxed structure is a little bit different
from the magnetic properties for experimental (not relaxed) structure, what
results should I believe?
Should I just believe the results that are close to experimental magnetic
properties?
Then why the expert Dr. Novak did not do the relaxation? Is it because the
relaxation for the known structures is really not needed?


All my best,
Jihoon Park


On Mon, Jul 21, 2014 at 2:59 PM, Víctor Luaña <
victor at fluor.quimica.uniovi.es> wrote:

> On Mon, Jul 21, 2014 at 02:16:27PM -0500, Jihoon Park wrote:
> > I am wondering if we must do the relaxation for all calculations.
> > I have found some first principles studies with experimental lattice
> > constants, including Dr. Novak's work "PRB 71, 1844422 (2005)."
> > Therefore, I need to know if the first principles calculations with
> > experimental lattice constants are reliable or in what case, it is good
> > enough or somethings.
> > Could anybody please give me some guidance?
>
> It depends very much on your intention. Optimizing an structure can be
> taken as a test of how appropriate is your calculation method for the
> system you are trying to analyze. The experimental value is the thing
> you are trying to reproduce, but not all experiments are done under
> the same precision, nor all experiments provide a well defined result.
>
> Remember that science is understanding, not only producing tables
> of numbers. Very simple models have been fundamental in science.
> For instance we owe our periodic table of the elements basically to
> ideas and concepts generated before quantum mechanics.
>
> It is not wrong, of course, the use a simple well defined recipe on a
> large collection of compounds trying to get some systematic rule.
>
> So, try to learn from the literature in your field and try to follow
> an unexploited road from the best starting point. Not a simple way but
> remember: It is easy to imagine a simple solution for a complex problem
> ... the pity is that most are wrong!
>
> Best regards,
>              Dr. Víctor Luaña
>
> --
>        \|/a  "After years of working on a problem the genius shout:
>       |^.^|     what an idiot I am ... the solution is trivial!'
> +-!OO--\_/--OO!------------------------------+-----------------------
> !            Dr.Víctor Luaña                   !
> ! Departamento de Química Física y Analítica   !
> ! Universidad de Oviedo, 33006-Oviedo, Spain   !
> ! e-mail:   victor at fluor.quimica.uniovi.es     !
> ! phone: +34-985-103491  fax: +34-985-103125   !
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