[Pw_forum] how to calculate U parameter

[TRINITE Virginie]

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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