[QE-users] Different implementations of the Hubbard 'U' between QE and VASP

[Shivesh Sivakumar]

Hello all,

While performing PBE+U calculations on a 2-D material, I wanted to try
using NCPPs and then PAW PPs. For the former, I obviously tried QE and for
the latter, VASP. The electronic bandstructures look very similar (the
parameters are completely the same, except for plane wave cutoffs, as you
might imagine) but the band gap is different.
With NCPPs, the Hubbard 'U' seems to suppress the band gap (compared to
U=0) whereas for VASP calculation, it seems to increase the band gap
(compared to U=0). Is there a qualitative explanation for this?

I am very sorry if this question is not totally appropriate for the forum
but I just want to know if conceptually, there are some differences in
implementation that I am missing out.

Best,
Shivesh Sivakumar
University of Washington
Seattle, WA-98105
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