[CP2K:1238] Re: hybrid DFT for bulk

Juerg Hutter hut... at pci.uzh.ch
Fri Jul 25 00:08:19 CEST 2008


Hi

just a few additional remarks.
You are aware that your system is pathological? It most likely
has a degenerate ground state (for non spin polarized) or
no gap for spin polarized calculations.
A quick sanity check for the total energy gives
8 * -0.5 = -4 a.u.
Looks like cp2k is less wrong than G03, if something like that
exists.

Try an infinite chain of He atoms or H2 molecules. There is a
small chance that you will get reasonable numbers.

regards

Juerg

----------------------------------------------------------
Juerg Hutter                   Phone : ++41 44 635 4491
Physical Chemistry Institute   FAX   : ++41 44 635 6838
University of Zurich           E-mail: hut... at pci.uzh.ch
Winterthurerstrasse 190
CH-8057 Zurich, Switzerland
----------------------------------------------------------


On Thu, 24 Jul 2008, molecule wrote:

>
> Hi, Teodoro
>
> I don't want to argue about the wording.
> I just did comparative calculations
> using cp2k and g03 for an infinite H chain (1A of separation).
> The settings are the same for both calculations:
> The unit cell contains 8 H atoms
> and its dimension is 8A x 8A x 8A.
> The basis set is 6-31G* and 4 shells are used for the periodicity.
> xc=b3lyp, k-sampling=\Gamma
>
> E(g03_PBC)= -27.6442625829 A.U.
> E(cp2k_PBC)= -4.426086805926252 A.U.
>
> Any comment on this?
>
> cheers,
> molecule
>
>
> On Jul 18, 9:28 pm, Teodoro Laino <teodor... at gmail.com> wrote:
>> Dear molecule,
>>
>> If you consider the gamma point sampling a numerical error.. well..
>> guess there's not too much one can comment.. but be cautious to do
>> such claims in a more aggressive audience!
>>
>> Moreover, keep in mind that Juerg also mentioned the 1/r problem for
>> the exact exchange.. and since your cell is small.. I wonder.. do you
>> consider
>> that a numerical problem as well?
>> Maybe you think that the whole story of long-range interactions is..
>> a numerical error? Eager to know your point of view..
>>
>> cheers,
>> Lost_somewhere_with_more_than_6_hours_delay.
>>
>> On 18 Jul 2008, at 23:09, molecule wrote:
>>
>>> However, the behavior looks more like a bug rather than the
>>> numerical errors caused by \Gamma-only sampling and the
>>> minimum images.
> >
>



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