[Wien] Coulomb correlation energy

[Florent Boucher]

Dear Igor,
I don't think there is an precise answer to your question, it really 
depends on the system your are looking for.
In the past, in a work we did with Pavel Novak, we were looking for O-K 
edge in a system Y2BaNiO5 containing Ni-O bonds. The main effect of the 
U was on the separation of the occupied and unoccupied d level of the 
Ni. As this d level are strongly mixed with the oxygen p level, the 
simulated EELS spectra is found strongly affected by the U value. So, in 
the present case, this is a way to find an approximately a correct U value.
However, last year I was studying a system LixMnO2 but in that case the 
effect of the U on the simulated O-K edge was not clear.
In the former case, we were in fact lucky as the O-p states were also 
mixed with the Y and Ba states in the conduction band. This is the 
position of the Ni unoccupied d band with respect to the Y and Ba states 
that we can check with EELS simulation by changing the U value.
Regards
Florent

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| Florent BOUCHER                    |                                    |
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