[Wien] volume optimization

[Zsolt Rak]

Let's suppose that the atomic positions (and lattice constants) are the
only information that I have. Is it physically justified to use LDA+U/GGA+U
to optimize the volume? or to tune the U value to reproduce the
experimental lattice constants? Also, is the DFT+U method based on the
variational principle?

On Fri, Mar 1, 2013 at 2:43 PM, Laurence Marks <L-marks at northwestern.edu>wrote:

> You need more a-priori information than this, for instance the bulk energy
> of related compounds for which a U is relevant. Tuning the U to reproduce
> known data is not by itself spectacular science.
>
> On Fri, Mar 1, 2013 at 1:24 PM, Zsolt Rak <zsolt.rak at gmail.com> wrote:
>
>>  I want to calculate the most accurate bulk energy and the a-priori
>> information I have are the atomic positions.
>>
>>
>>
>> On Fri, Mar 1, 2013 at 1:59 PM, Laurence Marks <L-marks at northwestern.edu>wrote:
>>
>>> 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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>>>
>>>
>>
>
>
> --
> 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
>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
>
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