[Pw_forum] DFT+U: about how to get U

[Agostino Migliore]

Hello

I am working on electron transfer in a solvated Fe2+/Fe3+ system. The
electron is (or "should be") always (i.e. for each water configuration)
essentially localized on one site, but a small portion (increasing near
the transition state) must be on the other site, just because of a nonzero
(although small) electronic coupling between the two sites. So, I wonder
if I should use two different U numbers for the two ions (e.g., that
obtained for the isolated oxidized (3+) site and the one for the reduced
site (2+), after check, without U, about the site that should turn out to
be essentially reduced/oxidized) or if I should use an average U for both
(neglecting the differences due to different water arrangements) and
"leave the transferring electron to reach its state", without biasing its
localization through different U's.

Regards,
Agostino Migliore