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.matti...@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.matti...@ism.cnr.it> > http://www.ism.cnr.it/en/staff/giuseppe-mattioli/ > ResearcherID: F-6308-2012 > > _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > > -- > This email was Anti Virus checked by Astaro Security Gateway. > http://www.sophos.com >
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