[Pw_forum] Clarification on Calculating U based on linear response

[Matteo Cococcioni]

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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