[Wien] volume optimization

[Laurence Marks]

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
>>
>> _______________________________________________
>> Wien mailing list
>> Wien at zeus.theochem.tuwien.ac.at
>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>
>>
>


-- 
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20130301/497223b1/attachment.htm>