[Wien] volume optimization

[Laurence Marks]

My two cents. Both LDA+U and GGA+U are wrong. That said, for f-/d- systems
they are often better than LDA/GGA for some properties. The question you
should ask yourself is what property are you trying to measure/predict, and
what a-priori information (reference state) do you have that can be used?

For instance, if I want to calculate a surface energy then I would tune the
U to give the most accurate bulk energy treating this as my a-priori
information; similarly if I wanted to calculate the elastic behavior of a
defect I would tune to the bulk elastic constants. In my opinion this is
the only justifiable approach.

On Fri, Mar 1, 2013 at 12:47 PM, Zsolt Rak <zsolt.rak at gmail.com> wrote:

>  Dear wien2k users,
>
> I am calculating the properties of several f-electron compounds. I would
> like to ask the users' opinion about the volume optimization in an f- or
> d-electron system: which way is better (or physically justified), with
> LDA/GGA or with LDA+U/GGA+U? In my opinion, the LDA+U/GGA+U techniques were
> developed to correct band energies of localized states, so there is no
> fundamental physical reason to use LDA+U/GGA+U methods for volume
> optimization. However, we observe a change in the lattice parameters when
> we go from LDA/GGA to LDA+U/GGA+U. Also, from a brief search of the
> literature we found that, in many cases, people tune the Hubbard-U
> parameter to reproduce the experimental lattice constants.
> I would appreciate further thoughts and insights into this issue.
>
> Thank you,
> Zs
>



-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu 1-847-491-3996
"Research is to see what everybody else has seen, and to think what nobody
else has thought"
Albert Szent-Gyorgi
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