If I am optimizing U value according to experimental bandgap for any system then if I am increasing U value then bandgap is increasing but it is not crossing experimental value till U=10.
So I want to ask at which U value I should stop. Is there any criteria or rule for maximum U value?
Shilendra
That's a really wierd question, as it doesn't have a single answer - it depends a lot on the approach you wish to undertake.
DFT+U is an interesting approach to describe strong on-site Coulomb interaction of localized electrons, which is known not to be very decently described by LDA or GGA approachs. This is made by means of a Hubbard-like term (see link for more info).
So, depending upon which type of methodology you're using - Leichenstein (see link) or Anasimov's (see link), the definition of U and J varies slightly in the way they are described.
Perhaps looking at one implementation of this method, such as GPAW, can provide you with a better insight.
https://en.wikipedia.org/wiki/Hubbard_model
http://dx.doi.org/10.1103/PhysRevB.52.R5467
http://dx.doi.org/10.1103/PhysRevB.57.1505
https://wiki.fysik.dtu.dk/gpaw/tutorials/tutorials.html
Thank you dear Alcides Simão and Kuntal Kabra for your reply.
I wanted to ask generally I have seen U values in literature for any system upto 8 eV and in rare case 9 or 10. So U value more than 10 eV is reasonable.
I was optimizing U value for W in WO3 system. I found without U it is showing 1.3 eV and with U=6 eV (varying 2, 3, 4 etc.) it is showing 1.54 eV and for 10 eV it is showing 1.75 eV. It is going 2.5 eV with U =16 eV. It was approaching experimental bandgap at higher U value 16 eV
And on increasing U value lattice constants are increasing and ground stat energy is also increasing like U=8 energy =-226.23 eV for U=10 energy = -212.56 ev etc.
So I want to ask here which U value I should take into account and higher value of U more than 8 is reasonable.
Any literature in which U value is more than 10 eV.
Shilendra
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