Dear F. Marsusi > Is this what one expected always from +U calculations,
As I told you before nothing can be considered as "expected" when you apply the U correction to a strongly hybridized sp2 system such as a pi- conjugated molecule or graphene. In my experience this is not a good idea, because you obtain, for example, a higher ionization energy (and this is right when you correct LDA/GGA delocalization errors, and in agreement with a correction with exact exchange like B3LYP or HSE) but also a lower electron affinity (and this is wrong, and the opposite behavior of a correction with exact exchange). So you are walking in "terra incognita" where nothing can be given for granted. HTH Giuseppe On Friday, February 10, 2017 08:38:37 PM FARAH MARSUSI wrote: > 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.â > > On Fri, 02/10/2017 08:09 PM, Giuseppe Mattioli <[email protected]> > 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"><[email protected]> > > http://www.ism.cnr.it/en/staff/giuseppe-mattioli/ > > ResearcherID: F-6308-2012 > > > > _______________________________________________ > > Pw_forum mailing list > > [email protected] > > http://pwscf.org/mailman/listinfo/pw_forum > > > > -- > > This email was Anti Virus checked by Astaro Security Gateway. > > http://www.sophos.com ******************************************************** - 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: <[email protected]> http://www.ism.cnr.it/en/staff/giuseppe-mattioli/ ResearcherID: F-6308-2012 _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
