[Wien] A basic question about GGA+U approach

[shamik chakrabarti]

Dear Prof. Peter Blaha,

            Thank you very much for your reply. I got my answer.

with best regards,

On Tue, Jun 26, 2012 at 11:19 AM, Peter Blaha
<pblaha at theochem.tuwien.ac.at>wrote:

> Yes, U depends on the type of atom, but of course also on the specific
> compound.
> For metallic Fe the U should be in the range of 0-2 eV at most, for some
> insulating compound with very localized states, it may go up to even 4-6
> (maybe even 8) eV.
>
> Am 26.06.2012 06:42, schrieb shamik chakrabarti:
>
>> Dear wien2k users,
>>
>>        We generally choose the value of U by fitting it with
>> experimental band gap or by calculating it through linear response
>> method. Now my question is that whether U is element specific or depends
>> on the composite in which the element reside? (*if I consider same
>>
>> magnetic configuration for all the composites I am referring here...as
>> antiferromagntism do produce a band gap even without applying any U*)
>>
>>
>> To make it more clear, say for Fe d, I have seen in literature, people
>> have used U=4.5 to 5 eV......in some of our calculation we have even
>> used U=6 eV for Fe d to obtain better electronic structure having closer
>> match with experimental observation. Hence it looks that U for Fe d
>> orbital can have value ranging from 4.5-6 eV...& that mean U is not
>> element specific rather it depends on the composite in which the element
>> exist (I again want to insist that if I consider same magnetic
>> configuration for all the composites). Am I right?
>>
>> with regards,
>>
>> --
>> Shamik Chakrabarti
>> Senior Research Fellow
>> Dept. of Physics & Meteorology
>> Material Processing & Solid State Ionics Lab
>> IIT Kharagpur
>> Kharagpur 721302
>> INDIA
>>
>>
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>>
> --
> Peter Blaha
> Inst.Materials Chemistry
> TU Vienna
> Getreidemarkt 9
> A-1060 Vienna
> Austria
> +43-1-5880115671
>
>
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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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