[Pw_forum] LSDA+U calculation on band gap

[Burak Himmetoglu]

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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