[Wien] volume optimization

[Zsolt Rak]

Dear Xavier, you said that you choose the Ueff value to reproduce one
property and then you use this Ueff value to predict the others. My
question is can I choose Ueff to reproduce a structural property (such as
the lattice constant or cell volume) and than use that value of Ueff to
predict electronic properties?



On Fri, Mar 1, 2013 at 3:04 PM, Laurence Marks <L-marks at northwestern.edu>wrote:

> If all you have are the atomic positions (and lattice constant) then the
> only unbiased approach would be to calculate the U, see
> http://www.wien2k.at/reg_user/textbooks/Constraint_U.pdf.
>
> N.B., the DFT+U method is variational for a fixed U, but I don't think it
> is variational as a function(al) of U.
>
> On Fri, Mar 1, 2013 at 1:58 PM, Zsolt Rak <zsolt.rak at gmail.com> wrote:
>
>>  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
>>>>>
>>>>>  _______________________________________________
>>>>> 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
>>>
>>> _______________________________________________
>>> 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
>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
>
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