[Pw_forum] Hubbard for oxygen

[Youssef Aharbil]

Dear Quantum espresso community,

It's well known that adapting the Hubbard model in DFT give a better
insight for the electronic structure on correlated materials, here the
systems with d and f shell localisation are corrected by applying a U
potential, but I don't understand why do we apply U also for oxygen,
unfortunately I can't find any reference (may be my research wasn't so
deep) giving more explanation.

Finally I would like to discuss the effect of hybridisation on U,
especially with mixed compounds where the oxygen electrons are shared on
between both Hubbard and non Hubbard atoms, from my experience on double
pervoskite the calculated value of U on Hubbard atoms including oxygen
using the linear response approach by cococcioni et al  overestimate the
band gap .

>From my point of view I think that the value of U must be proportional to
the number of electron only shared between Hubbard atoms and the oxygen.

Thanks in advance.

Youssef Aharbil
Faculty of sciencs ben msik.
Morocco
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