[QE-users] Constrained DFT (Hubbard alpha approach)

[Lorenzo Paulatto]

> The main problem I encounter is "double counting" of electrons, i.e. the 
> total number of electrons is not 2 but over 3 and the "most integer" 
> occupation I can get for H1 is ~1.96 (ok, close enough to 2) but only 
> for fairly large distance H-H. I attached a plot and the run-script, if 
> anyone could give it a glance and tell me if this is totally wrong or a 
> little bit right I would be very grateful!

Hello,
I don't know if this can solve your problem, but the H-H distance in H2 
is very small (around 1.4 bohr, 0.7 Å), much smaller than twice the 
cutoff radius used in most pseudopotentials available. This introduces 
quite sizable errors, and may be the origin of the double-counting you see.

When working in the PAW implementation, I had generated a 
pseudopotentials that was a bit harder than usual (~120Ry) but should 
have no overlap in a realistic distance range. I'm attaching the file 
(re-generated with a recent qe version) in case you want to try it.




-- 
Lorenzo Paulatto - Paris

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