[QE-users] Regarding U in self-consistant and site dependent

[Matteo Cococcioni]

Dear Anish

Il giorno mar 23 nov 2021 alle ore 07:10 Anish Das <anishdas39 at gmail.com>
ha scritto:

> Dear experts,
>
> I am interested in calculating Hubbard-U in self consistent and and site
> dependent manner as i am dealing with local point defect and expecting
> different charged states near the defect. First, I activated the U
> calculation machinaries by applying very small U value (10^-8).Then I
> perturbed the inequivalent open-shell Hubbard sites and got 1st shot of U
> values (for different sites). Then I am supposed to use new values of U and
> again go for the 2nd shot U calculation.
>
> Now my questions are.
>
> 1) Should i relax the structure with U values calculated from 1st shot
> then go for the 2nd shot? Or i just simply plugin the new U, do SCF and go
> for the 2nd shot U-calculation. Dr. Iurii Timrov mentioned to relax the
> structure everytime with new U values in his paper. But my structure is
> large and has 52 Hubbard sites (159 total atoms).
>
>
there is no rule. depends on your system and on what you want to do. In
principles there is always some depenence of U on the structure (and
viceversa). How large this dependence is nobody knows before testing.


> 2) As i mentioned earlier that my system has 52 inequivalent Hubbard
> sites, so 1st i perturbed the all sites and get the 1st shot of U. Then i
> relaxed the structure with new U's. Now after the relaxation when i check
> the inequivalent Hubbard sites for 2nd shot U calculation (by hp.x), it is
> now showing i have 48 Hubbard sites (instead of 52) to be perturbed. My
> question is, should i need to perturb the 52 sites (determined during the
> 1st shot) or 48 sites (determined during 2nd shot calculation)?
>

probably your crystal has become more symmetric and Hubbard atoms got a
more similar environment to one another. that can happen. Probably your
starting structure was a bit disordered and its now going to the near
symmetric minimum of energy. Just guessing.

Please add your affiliation.

Hope this helps.

Matteo


>
> Thanking you
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-- 
Matteo Cococcioni
Department of Physics
University of Pavia
Via Bassi 6, I-27100 Pavia, Italy
tel +39-0382-987485
e-mail matteo.cococcioni at unipv.it <lucio.andreani at unipv.it>
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