[Pw_forum] GGA+U

[Giuseppe Mattioli]

Dear F. Marsusi
First of all you are not providing any detail of your system, so we cannot even guess what is "natural" for it.
However, you are using the Hubbard U correction in a semiempirical way, and there is therefore no way to choose the U value but that reproducing some 
measured parameter, and not very much to do if unexpected or strange results appear at a given (unphysical?, problematic?) U value.
In my experience the application of U to organic molecules has been always problematic due to the strong hybridization between C 2s and C 2p orbitals, 
and to the application of the correction to 2p orbitals only.
HTH
Giuseppe

On Friday, February 10, 2017 07:25:10 PM FARAH MARSUSI wrote:
> Dear all,
> 
> By GGA+U as implemented in QE, the correct magnetization (M) and band gap was obtained. The correct U value for each atom was obtained by intensive
> step by step runs to reach gradually the experimental M value, and therefore band gap. All results are OK till now (the U value itself also= 3.4 eV
> for carbon and fluorine is acceptable ). However, by enlarging the obtained U value a bit (to 3.7 eV), the predicted M come back to that of pure
> GGA. Is it natural, or a problem exist?
> 
> 
> Best regards,
> F. Marsusi,

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   Giuseppe Mattioli                            
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