[Pw_forum] lda+U abinitio U

[Matteo Cococcioni]

Hi Lorenzo,

the two tutorial should be quite equivalent, although the one Federico
found is more recent and probably I updated some details.

Regarding your questions: as far as I understand you are only interested in
U on one specific atomic species of your materials. You could do that by
doing two perturbations: one on the atom you are interested in, the second
on all the other atoms (which you treat as a "macro-atom") at the same
time. Of course the occupation of this second "extended atom" is the sum of
the occupations of the atoms it is composed by. you then construct a 2x2
response matrix that, once inverted, should give you the U you are looking
for (throwing away the one for the "macro-atom").
This only limits the number of perturbation but still requires a supercell
of sufficiently large size.

We are working on a way to make the whole procedure more efficient, through
automatizing the linear-response, but the code is not ready yet.

Best,

Matteo

On Fri, Sep 2, 2016 at 5:55 PM, Lorenzo Paulatto <
lorenzo.paulatto at impmc.upmc.fr> wrote:

> Hello,
> I have a question about how to compute the abinitio U, I'm following the
> online Santa Barbara 2009 tutorial (and trying to use the script therein)
> and
> PRB 71, 35105 (2005).
>
> I have a system that is not very large but quite heavy to compute, and have
> several atomic species (3 at first, then 4) but only one is problematic,
> as it
> is could be Cerium or other Lanthanoids.
>
> It would be quite anoying and very cpu time consuming for me to properly*
> compute U by finite response for all the species, but I'm not sure that
> 1. it is possible with the available toolchain
> 2. it makes sense
>
> Also, if somebody (e.g. Matteo) has some more recent and/or more user
> friendly
> code to compute dalpha/dn I'm a taker.
>
> thank you for your help!
>
> *) by properly I mean take care that it is converged with the supercell
> size
>
> --
> Dr. Lorenzo Paulatto
> IdR @ IMPMC -- CNRS & Université Paris 6
> +33 (0)1 44 275 084 / skype: paulatz
> http://www.impmc.upmc.fr/~paulatto/
> 23-24/4é16 Boîte courrier 115,
> 4 place Jussieu 75252 Paris Cédex 05
>
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