[Pw_forum] Clarification on Calculating U based on linear response

[Joshua Davis]

Thank you so much for your help.  It really cleared things up.

----------------------------------------------------------------------------------------------------------------
Joshua D. Davis

Graduate Assistant
Department of Chemistry
Michigan State University

East Lansing, MI 48824
-----------------------------------------------------------------------------------------------------------------

On Tue, Mar 3, 2015 at 3:40 AM, Matteo Cococcioni <matteo at umn.edu> wrote:

> Dear Joshua
>
> On Mon, Mar 2, 2015 at 4:27 PM, Joshua Davis <davis101 at chemistry.msu.edu>
> wrote:
>
>> Dear QE Users
>>
>> I want to know how to calculate U based on linear response
>> <http://journals.aps.org/prb/abstract/10.1103/PhysRevB.71.035105>, but
>> I  am having trouble understanding what occupation values to use from a
>> calculation for a response matrix.
>>
>> I have fallowed the tutorials
>>
>>
>> http://media.quantum-espresso.org/santa_barbara_2009_07/slides-exercices/Handson_ldau.pdf
>>
>> and
>>
>> http://hjklol.mit.edu/content/calculating-hubbard-u
>>
>>
>>
> you have to use the trace of the occupation matrix.
>
>
>
>> Do I use the Trace of the d-electron occupation matrix (like in the first
>> link) or am I to use sum of all the elements of the matrix (like in the
>> second link)?
>>
>> Secondly when calculating U, if the atoms that require a U are not very
>> close to each other, can you get away with not calculating the off-diagonal
>> response matrix elements and just invert the diagonal response matrix
>> elements directly?
>>
>
>
> I guess it depend on the system you are considering. just try in one case
> and see how results compare.
>
> Matteo
>
>
>
>>
>> I am using QE 5.1.
>> Thanks for any help
>>
>> ----------------------------------------------------------------------------------------------------------------
>> Joshua D. Davis
>>
>> Graduate Assistant
>> Department of Chemistry
>> Michigan State University
>>
>> East Lansing, MI 48824
>>
>> -----------------------------------------------------------------------------------------------------------------
>>
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>
>
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