[Pw_forum] how to calculate U parameter

Giuseppe Mattioli giuseppe.mattioli at ism.cnr.it
Fri Jan 9 16:42:18 CET 2015 

> Did you think that with new version of the code, it will be more manageable

Not really, but you can try to enable the adaptive_thr for the inner scf, and to (carefully, because you have a metal) lower the ecutrho cutoff to 
ecutwfc~2*ecutwfc instead of using the default 4*ecutwfc value. But if you have more than 100 electrons EXX is still quite expensive, and if you have 
more than 1000 electrons (at Gamma only) EXX is not an option...
HTH
Giuseppe

On Friday, January 09, 2015 11:21:01 AM TRINITE Virginie wrote:
> Dear Matteo and Guiseppe.
> 
> Thanks for yours answers. I have try EXX functional some time ago, and It was so lengthy that I have forget about it (It was a metal, and I have to
> use high number of q points to converge the calculation, without to mention that with the semicore states the pseudopotential also need a high
> energy cut off).
> Did you think that with new version of the code, it will be more manageable , I have not look of the recent advances from this part?
> 
> 
> De : pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] De la part de Giuseppe Mattioli
> Envoyé : vendredi 9 janvier 2015 11:00
> À : pw_forum at pwscf.org
> Objet : Re: [Pw_forum] how to calculate U parameter
> 
> 
> 
> 
> Dear Virginie
> 
> Short answer: It isn't.
> 
> Realistic answer: Use an EXX functional if you can afford it.
> 
> Hopeful answer: It will be possible when the DFT+U+V code is released.
> 
> Very hopeful answer: It would be possible whether the ACBN0 U-based hybrid functional was released.
> 
> 
> 
> Dear Swati
> 
> There is no way to calculate a linear response U for the fully occupied Zn 3d shell. Perform a series of calculations to find semiempirical values
> of U(Zn) and U(Se) which are suitable for your purposes. For example, try to find U values which reproduce the fundamental band gap of ZnSe
> *together with* acceptable estimates of its ionization energy and electron affinity. Remember to modify the source code, as pointed out by Matteo,
> in order to include Se within the "U-able" atoms.
> 
> 
> 
> HTH
> 
> Giuseppe
> 
> On Friday, January 09, 2015 10:17:50 AM TRINITE Virginie wrote:
> > Dear All
> > 
> > 
> > 
> > I have a related question, coming from elements with semicore states :
> > 
> > Is it possible to have more that one orbital by atoms corrected by the U?
> > 
> > I was thinking that maybe for 3d and 4d elements, it will be meaningful to correct not only the d part but also the semicore states that are very
> > 
> > localized.
> > 
> > Best Regards
> > 
> > 
> > 
> > Dr Virginie Trinite
> > 
> > ---------------------------------------
> > 
> > Modeling Infra-Red Lasers and Detectors
> > 
> > III-V Lab THALES Research& Technology, France
> > 
> > 
> > 
> > Campus Polytechnique
> > 
> > 1, avenue Augustin Fresnel 91767 Palaiseau cedex France
> > 
> > 
> > 
> > De : pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] De la part de Matteo Cococcioni
> > 
> > Envoyé : vendredi 9 janvier 2015 00:06
> > 
> > À : PWSCF Forum
> > 
> > Objet : Re: [Pw_forum] how to calculate U parameter
> > 
> > 
> > 
> > 
> > 
> > Dear Swati,
> > 
> > 
> > 
> > one possibility is to compute U from linear response as we proposed some year ago in PRB 71 35105 (2005). You can also find a tutorial on this on
> 
> > the webpage:
> http://media.quantum-espresso.org/santa_barbara_2009_07/.
> 
> > As for Se do you really need to use U on it? if so, you have to update the routines set_hubbard_l.f90 and tabd.f90 in order to tell the code what
> > 
> > orbital shoudl be corrected by U and how many electrons it should put on them at the beginning of calculation. These routines are contained inside
> > 
> > the flib and PW/src/ directories of the code which you then need to recompile.
> 
> Best regards,
> 
> > Matteo
> > 
> > 
> > 
> > On Thu, Jan 8, 2015 at 6:42 PM, Swati Khatta <swati.khatta at gmail.com<mailto:swati.khatta at gmail.com>> wrote:
> > 
> > Dear all,
> > 
> > I would like to do calculations with DFT+U of ZnSe material using Quantum esspresso. As per I know there is different U for each distinct type of
> > 
> > hubbard atom.And typical value of U is rarely larger than 7-8 eV and in most case it lies between 0<U<5. but how do we know that which value of U
> > 
> > satisfied for Zn atom .Is there we do any type of convergence to calculate U parameter.
> 
> And in case we include U parameter for Se the error has
> 
> > ocurred ' pseduopotential is not inserted yet'. So is it sufficient to not include U parameter for Se to do DFT+U calculations for ZnSe. Regards
> > 
> > swati khatta
> > 
> > panjab University
> > 
> > chandigarh
> > 
> > 
> > 
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> > 
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> > 
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> Giuseppe Mattioli
> 
> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
> 
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********************************************************
- Article premier - Les hommes naissent et demeurent
libres et ègaux en droits. Les distinctions sociales
ne peuvent être fondèes que sur l'utilitè commune
- Article 2 - Le but de toute association politique
est la conservation des droits naturels et 
imprescriptibles de l'homme. Ces droits sont la libertè,
la propriètè, la sùretè et la rèsistance à l'oppression.
********************************************************

   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
   v. Salaria Km 29,300 - C.P. 10                
   I 00015 - Monterotondo Stazione (RM)          
   Tel + 39 06 90672836 - Fax +39 06 90672316    
   E-mail: <giuseppe.mattioli at ism.cnr.it>
   http://www.ism.cnr.it/english/staff/mattiolig
   ResearcherID: F-6308-2012

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