[CP2K:1849] Re: problem with total charge density and graphite calculations

[Juerg Hutter]

>
> 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.

Hi

PBE is known to have already some attractive potential in the intermediate
range. You can also see that from the general constant in the Grimme
potential that is set to 0.75 for PBE.
This is the reason why usually people use a revised form of PBE
together with vdW corrections (see for example the papers by the Lunqvist 
group).

regards

Juerg Hutter

>
> 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
> >
>