[CP2K:1238] Re: hybrid DFT for bulk

Teodoro Laino teodor... at gmail.com
Thu Jul 24 22:52:29 CEST 2008


Molecule,
do you mean you are using GAPW? I'm impressed.
Anyway.. even before trusting your GAPW results (and there are few  
people here that
can witness how NON TRIVIAL is to do a GAPW calculation) you remember  
what Juerg
told you?
We do NOT have the long range for the exact exchange (yet) !!

Have no idea what Gaussian has implemented.. but comparing numbers in  
this way (i.e. without
having an idea of what you are comparing!!) is not a good attitude.

We may discuss about the correctness of periodic B3LYP calculations  
with GAUSSIAN (I guess
there are plenty of nice *features* you would discover)..
but if you trust them.. please use Gaussian.. since with CP2K at the  
moment you don't
have the long-range part of the exact exchange (hopefully should be  
clear now).

Teo

On 24 Jul 2008, at 22:41, 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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