[Pw_forum] GGA+U

[FARAH MARSUSI]

Dear Giuseppe,

Many thanks for your quick response. As you have correctly guessed, the system is an organic material (fluorinated graphene). From U=0 to 3.4, M is increasing gradually up to the expected value, M remains constant till U=3.6 eV, then by increasing U, again M is reduced very soon to zero. Is this what one expected always from +U calculations, when goes up further from the optimum U value? From your answer, it is concluded to be a strange behavior due to the organic nature of this material.

Best regards,
F. Marsusi,

Amirkabir University of Technology.​
On Fri, 02/10/2017 08:09 PM, Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it> wrote:
> Dear F. Marsusi
> First of all you are not providing any detail of your system, so we cannot even guess what is "natural" for it.
> However, you are using the Hubbard U correction in a semiempirical way, and there is therefore no way to choose the U value but that reproducing some 
> measured parameter, and not very much to do if unexpected or strange results appear at a given (unphysical?, problematic?) U value.
> In my experience the application of U to organic molecules has been always problematic due to the strong hybridization between C 2s and C 2p orbitals, 
> and to the application of the correction to 2p orbitals only.
> HTH
> Giuseppe
> 
> On Friday, February 10, 2017 07:25:10 PM FARAH MARSUSI wrote:
> > Dear all,
> > 
> > By GGA+U as implemented in QE, the correct magnetization (M) and band gap was obtained. The correct U value for each atom was obtained by intensive
> > step by step runs to reach gradually the experimental M value, and therefore band gap. All results are OK till now (the U value itself also= 3.4 eV
> > for carbon and fluorine is acceptable ). However, by enlarging the obtained U value a bit (to 3.7 eV), the predicted M come back to that of pure
> > GGA. Is it natural, or a problem exist?
> > 
> > 
> > Best regards,
> > F. Marsusi,
> 
> ********************************************************
> - Article premier - Les hommes naissent et demeurent
> libres et égaux en droits. Les distinctions sociales
> ne peuvent être fondées que sur l'utilité commune
> - Article 2 - Le but de toute association politique
> est la conservation des droits naturels et 
> imprescriptibles de l'homme. Ces droits sont la liberté,
> la propriété, la sûreté et la résistance à l'oppression.
> ********************************************************
> 
>    Giuseppe Mattioli                            
>    CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
>    v. Salaria Km 29,300 - C.P. 10                
>    I 00015 - Monterotondo Stazione (RM), Italy    
>    Tel + 39 06 90672342 - Fax +39 06 90672316    
>    E-mail: " target="_blank"><giuseppe.mattioli at ism.cnr.it>
>    http://www.ism.cnr.it/en/staff/giuseppe-mattioli/
>    ResearcherID: F-6308-2012
> 
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
> 
> --
> This email was Anti Virus checked by Astaro Security Gateway. http://www.sophos.com
> 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20170210/e82701c6/attachment.html>