[Wien] volume optimization

Zsolt Rak zsolt.rak at gmail.com
Fri Mar 1 21:12:58 CET 2013


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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