[Wien] A basic question about GGA+U approach

[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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