problem with total charge density and graphite calculations

[Andrzej]

Thanks for response. Well it is why I decided to multiply the unit
cell.

In my original crystal, which is an insulator, and the layers are
binded by vdW interaction I also have an attraction between layers,
when it is calculated using pure PBE - similarly as I observed for
graphite. It worries me, because it looks as an artificial effect. If
I have an artificial attraction using PBE, the binding energy obtained
from PBE+D is oversetimated.

On Mar 10, 1:05 pm, Matt W <MattWa... at gmail.com> wrote:
> Hi,
>
> well one issue is when does the system become metallic?  Possibly in
> some of the smaller systems there is enough of an artificial band gap
> for you to reach convergence ... but it's not obvious to me why it
> works at all.
>
> Not sure why you're losing electrons though.
>
> Matt