[Wien] Need advice for modeling the band gap in a charge transfer insulator

[Shamik Chakrabarti]

Dear Prof. Peter Blaha Sir,

     The material is ferrimagnetic and we have include that magnetic
ordering by properly editing case.inst file. Yes we have not tried mbj
potential and that may be an alternative. Our calculation is going on a
system having 56 atoms/supercell and it generally take around 80 iterations
to converge for GGA+U (ferrimagnetic) calculation. In this regard do you
think that mbj potential can be a better alternative for our ferrimagnetic
insulating system?

Looking forward to your response.

with best regards,

On Tue, Oct 25, 2011 at 7:09 PM, Peter Blaha
<pblaha at theochem.tuwien.ac.at>wrote:

> Are you sure, your LDA+U calculations are done correctly ?
> You have to make spin polarized calculations with the correct magnetic
> order.
> Often a FM state is metallic, while the proper AFM state is insulating.
>
> The full hybrid-DFT method will be available in the next release.
> However, this is an expensive method and you cannot apply it to large
> systems. At least you will need a powerful cluster with many nodes ...
>
> PS: Have you done mBJ calculations ? In our experience this is at least as
> accurate as hybrid DFT at a fraction of cpu-time when you need only the
> bands/DOS.
> It also works well for "correlated" electrons and in addition it does not
> have
> a parameter (like the alpha in hybrid-DFT or the U in LDA+U).
>
>
> Am 25.10.2011 12:14, schrieb David Tompsett:
>
>> Hi Shamik,
>>
>> DFT+U can sometimes give a reasonable description of materials with some
>> charge transfer (possibly also some Mott) insulating character eg. NiO. But
>> it seems that in your case
>> itinerant states are important to the band gap and in that case using
>> Hybrid functionals that include exchange between all states (including
>> itinerant ones) often helps eg. MnO. I
>> think a full hybrid functional set will come out in an upcoming version of
>> Wien2k?
>>
>> Some references:
>> Tran et al.
>> PHYSICAL REVIEW B83,235118 (2011)
>>
>> Best,
>> David.
>>
>> 2011/10/25 shamik chakrabarti <shamikphy at gmail.com <mailto:
>> shamikphy at gmail.com>>
>>
>>
>>
>>    Dear wien2k users,
>>
>>                                 We all know that LSDA (or GGA)+U can be
>> used successfully for a Mott-Hubbard insulator. Anisimov et al. [PRL 99,
>> 156404 (2007)] have described
>>    that for a charge transfer insulator we need to use LDA+DMFT for
>> modelling their band structure properly. Now my question is :
>>
>>    (1) Is their any option in wien2k by which we can use LDA+DMFT?
>>
>>    (2) In our calculation after applying GGA+U (U for d orbital of TM) we
>> saw that although there are a band gap between spin up & spin dn d DOS of
>> transition metal, there are
>>    ligand (O p) DOS at Fermi Energy which is making our material metallic
>> while experimentally it is an insulator [conductivity ~ 10^(-7)]. Here
>> should we apply some value of U
>>    (say 0.15 Ry) for O p orbital also?
>>
>>    (3) Any other advice regarding to this problem will be highly
>> appreciated.
>>
>>    Thanks in advance.
>>
>>    yours faithfully,
>>    --
>>    Shamik Chakrabarti
>>    Senior Research Fellow
>>    Dept. of Physics & Meteorology
>>    Material Processing & Solid State Ionics Lab
>>    IIT Kharagpur
>>    Kharagpur 721302
>>    INDIA
>>
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>
> --
>
>                                      P.Blaha
> ------------------------------**------------------------------**
> --------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
> Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/**
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-- 
Shamik Chakrabarti
Senior Research Fellow
Dept. of Physics & Meteorology
Material Processing & Solid State Ionics Lab
IIT Kharagpur
Kharagpur 721302
INDIA
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