[Pw_forum] how to calculate U parameter

[Giuseppe Mattioli]

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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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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