[Pw_forum] LSDA+U calculation on band gap

[Burak Himmetoglu]

Hello Peng,

Yes, in principle U is different for different states. The difference might
be small, but it can be very critical in your case, since the AFM and FM
gaps are very close.

Best regards,

Burak

On Wed, Aug 8, 2012 at 2:59 PM, Peng Chen <pchen at ion.chem.utk.edu> wrote:

> Dear Dr. Burak,
>
> U is different for AFM and FM states? The problem now is I can not make
> the U calculation correct.  Dr. Matteo is helping me with great patient,
> but still no luck now.
>
>
> On Wed, Aug 8, 2012 at 2:49 PM, Burak Himmetoglu <himm0013 at umn.edu> wrote:
>
>> Hello Peng,
>>
>> One can compute U for the AFM and FM states separately using linear
>> response. Then, using the calculated U values for each state, you can
>> recompute the gaps. This approach might resolve the issue.
>>
>> Best regards,
>>
>> Burak
>>
>> On Wed, Aug 8, 2012 at 1:00 PM, Peng Chen <pchen at ion.chem.utk.edu> wrote:
>>
>>> Dear All,
>>>
>>> According to the experiments, the material's ground state is afm and the
>>> band gap is ~2.30 eV in 4K.
>>> In the magnetic field, the spin moments are aligned in the field
>>> direction (we call it "fm state") and the
>>> band gap is ~2.34 eV. But from the calculation results, when U>=5 eV,
>>> the fm spin up gap is less
>>> than that of afm state which is different from experimental results. (I
>>> guess we should choose spin
>>> up gap to represent fm state gap since spin down gap is larger). From
>>> the calculated gap value,
>>> U=8 eV is close to experimental results, but the gap in fm state is
>>> less. Please let me know what
>>> I can do to improve the results?
>>>
>>>
>>> U    afm gap     fm spin up    fm spin down
>>> 4     1.49           1.723             1.731
>>> 5     1.81           1.77                 2.01
>>> 6     1.922         1.912              2.273
>>> 8     2.265         2.076              2.634
>>>
>>>
>>> --
>>>   Best Regards.
>>>         Peng
>>>
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>>>
>>>
>>
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>
>
> --
>   Best Regards.
>         Peng
>
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