[Wien] BJ vs. mBJ

[tran at theochem.tuwien.ac.at]

Both mBJ and unmodified BJ are potentials.
For the 2nd second, I would just say: use the potential
which leads to results that are the most pleasing.


On Fri, 15 Jan 2016, delamora wrote:

> Thank you Dr. Tran,
>          In the setting of the mBJ I used;
> init_mbj
>
> Which has different parametrizations of mBJ:
>
> 0:    Original mBJ values (Tran,Blaha PRL102,226401) (default)
> 1:    New parameterization (Koller etal, PRB85, 155109)
> 2:    New parameterization for semiconductors (gaps up to 7 eV)
> 3:    Unmodified BJ potential (Becke,Johnson J.Chem.Phys 124,221101
>
>       I used
>                      0:    Original mBJ values
>                      3:    Unmodified BJ potential
> So my question was; in option '3:' it is still a potential and not a functional and it does not work if :FER is not in the gap?
>         This is because I have a system with Sm which has a peak in the gap and :FER is in that peak, so if the "Unmodified BJ potential" was more "flexible" than the "Original mBJ values" then I could use this option.
>
> I did the calculations again and I got for the gap:
> without BJ    5.05eV
> with mBJ       8.5eV
> with unmodified BJ    5.8eV
>
> but this time I did the things right and, for NaCl, I got :FER at the top of the valence band, which in earlier WIEN2k versions would move into the gap.
>
>     So, my second question is; Which is better mBJ or 'unmodified BJ'?
>
> Pablo
> ________________________________________
>
> If a system has a gap, then the Ef (:FER) is set at the top of the
> valence band maximum. Since there is for sure a gap in NaCl, whatever
> is the used potential, then I don't understand your statement about
> unmodified BJ. The value of :FER in case.scf should be equal to
> the valence band maximum (grep for :BAN00008: in case.scf). If not
> there is something wrong in your calculations.
>
> F. Tran
>
> On Thu, 14 Jan 2016, delamora wrote:
>
>>
>> WIEN2k users,
>>
>>         I am trying the mBJ potential and the Unmodified BJ potential, so I took NaCl as an example, so I get for the gap;
>>
>> without BJ:      5eV
>>
>> mBJ:                 8.2eV, and Ef is at the bottom of the gap
>>
>> Unmodified BJ: 6eV, Ef is not at the bottom of the gap
>>
>>         With these 3 very different values which one is the best; mBJ or Unmodified BJ?
>>
>>
>>         I suppose that the Unmodified BJ is still a potential and cannot be used when Ef is not in the gap.
>>
>>
>>             Pablo
>>
>> I am using WIEN2k 14.2
>>
>>
>>
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