In , it says:
/In Refs. [77,82] we showed that a correct description of the band gap
and electric-field gradient (EFG) in Cu2O could only be achieved with
the hybrid functionals, while the results////obtained with the LDA, GGA,
LDA+U, and mBJ methods////were qualitatively wrong./
In TABLE IV of , GGA (PBE) gap is 0.53 eV. In TABLE I of , mBJ
gap is 0.82 eV.
I'm not seeing a WIEN2k value reported for GGA+U, but maybe it is close
to the 0.79 eV gap (AMF, U = 8 eV) LDA+U calculation  or the 0.67 eV
gap (with U of 7 eV) GGA+U calculation by VASP .
The 0.53 eV, 0.82 eV, and 0.67 eV above round up to be approximately 1.0
eV, which is around the 1.0 eV that you report.
On the other hand, GGA+U+mBJ calculation may give 1.60 eV .
 http://dx.doi.org/10.1063/1.4798706 (TABLE I)
On 8/18/2017 9:14 PM, halim said wrote:
Dear Prof. Tran,
Thank you for your answer, I mean withing GGA, mBJ-GGA, and GGA+U, I
found the energy gap around 1 eV.
In principle the experimental gap is about 2 eV.
Where is the problem?
Thank you for your help.
Le Vendredi 18 août 2017 23h29, "t...@theochem.tuwien.ac.at"
<t...@theochem.tuwien.ac.at> a écrit :
What do you mean by 1 eV? Does it mean that all
gaps are at exactly 1.0 eV or in a range like 0.5-1.5 eV?
You can compare your results with those in these two articles:
Cu2O is a special case for which mBJ and GGA+U are not really
better than GGA.
On Friday 2017-08-18 21:42, halim said wrote:
>Date: Fri, 18 Aug 2017 21:42:24
>From: halim said <halim_sai...@yahoo.fr <mailto:halim_sai...@yahoo.fr>>
>Reply-To: A Mailing list for WIEN2k users
>Subject: [Wien] problem of energy gap within mBJ
>Dear Professor Peter Blaha, Tran and Wien2k users,
>I have computed the energy gap for Cu2O by using GGA, mBJ, and GGA+U,
I got same energy gap of 1 eV.
>In principle by using mBJ, the energy gap should be increased close
to expermimental value around 2 eV.
>Why mBJ is giving same value as GGA and it is not improved? even I
tried GGA+U and the same problem and no thing was changed for all
>I would be thankful for your suggestion and answer to solve the problem.
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