[QE-users] Consequence of incorrect setup of electron configuration.

[Evgeny Permyakov]

Dear Eduardo!
 Thanks for you answer, I think, I got satisfying answer for my first question.

> A/ If supercell B is the double of A, then you have an even number of
> electrons, unless you charge the system.
> I think that you cannot have such band with just one electron in supercell B,
> assuming the supercell B is not relaxed after duplication of A.

It might be hard to find one for a solid with dense packing, but I'm
working with ribbon-like models of a semiconductor with reasonably
wide band gap. There, two families of HOMOs associated with edges
appear. and it is entirely possible to have a supercell B with two
bands on the opposite sides of the ribbon to have one electron each.
In this case it should be possible to have an even number of electrons
in supercell B, but still have two unconnected bands with one electron
each. Isn't it so?

> Also, note that to make A and B equivalent, for supercell A you need
> to duplicate the number of k-points, therefore you end
> with the same number of occupied energy levels and the same energies,
> just distributed in a different fashion.

I usually run Gamma-point calcuations, and my supercells are fairly
large (10+ A in each direction). I read in some textbooks/tutorials
that for such large supercells there is no usually need to use more
than one k-point, and I got chemically reasonable values before. Am I
wrong?


Best regards

Evgeny Permyakov.