[Wien] A basic question about GGA+U approach

[Peter Blaha]

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