[CP2K:1880] Re: Grimme correction and supercell

[Teodoro Laino]

The neighbor list is always built across all possible periodic images 
included within the CUTOFF specified
for the dispersion (as long as you don't have PERIODIC NONE in the &CELL 
section! this case would
explain the problem then..)
.
The problem must be somewhere else..
Could you please post a simple input file for both cases (111 and 422) ?
Thanks
Teo

Axel wrote:
>
> On Mar 16, 12:54 pm, Andrzej <kwa... at o2.pl> wrote:
>   
>> Dear users,
>>
>> I performed some calculation for graphite, just for testing some
>> features.
>> Here are some results obtained from single point calculations made for
>> experimenrtal crystal structure under periodic conditions.
>> Calculations were performed for single unit cell (111), and extended
>> unit cells: 222, 332 and 442.
>>
>> Here are values of dispersion (Grimme) energy per C atom.
>>
>> 111: -0.004719
>> 222: -0.0041627
>> 332: -0.00405803
>> 442: -0.00405803
>>
>> As the calculations were performed under periodic conditions I would
>> expected that all these values should be the same. Grimme correction
>> is purely classical expression independent of electron density,
>> cutoff,  lack of k-point sampling and so on.
>>     
>
> but it is not independent of minimum image convention and
> the classical cutoff. i haven't checked the cp2k implementation,
> but the equivalent code in cpmd would provide an option to
> compute the real space interactions across multiple copies of
> the principle unit cell, so that for small unit cells, you
> would still be able to compute those interactions up to a
> significant distance beyond the restrictions of using only
> the closest image.
>
> cheers,
>    axel.
>
>   
>> I will be grateful for any comment.
>>
>> Andrzej
>>     
> >
>