Hi Gregorio
When you talk about Pi-stacking... do you mean Van der waals interactions?
If this is the case remember the drawbacks of:
LDA: cancellation of errors with a near overbinding tendency
GGA: VdW interactions are totally neglected
Please, consider the use of the new VdW xc-potential introduced in the new
versoin of siesta.
Regards
Ricardo
p.s.: it has nothing to do with BSSE
> Ok, thanks.
> I tried with TZP basis set, but the results don't improve enough.
> Respect to use BSSE, I agree with you about the problem to use with my
> system, since the are two indentical molecules (interconvertible by
> symmetry) in the unit cell.
> Finally, I don't know how to include diffuse functions in SIESTA.
>
> Thanks
>
> Gregorio
>
>
> El 03/06/2010 12:49, Herbert Fruchtl escribió:
>> If you mean counterpoise corrected geometry optimisation, that's
>> tricky, and definitely not implemented in SIESTA. Counterpoise is only
>> really straight-forward for dimers (or at least small numbers) of
>> fairly rigid molecules. In a crystal, you would have to make sure that
>> your supercell is big enough (you can't CP correct the interaction of
>> a molecule with its image), and I don't know the implications for
>> K-points (my first inclination would be to say if you need more than
>> one K-point, your system is too dense for counterpoise to be
>> meaningful).
>>
>> Have you tried adding diffuse functions? BSSE is a consequence of the
>> incompleteness of localised basis sets. If you describe the
>> wavefunction far away from the nuclei better, it should improve, but I
>> don't know how quickly.
>>
>> HTH,
>>
>> Herbert
>>
>> Gregorio García Moreno wrote:
>>> Hi all
>>> I am studing polymers pi-stacked. I have obtained good crystal
>>> parameters, except for the pi-stacking distance, which is smaller
>>> than experimental data. Here, you recomended me that I should use TZP
>>> and BBSE. I have tried with TZP, but the results do not improve
>>> respect to DZP. However, I have searched in literature, and to apply
>>> BSSE could solucionate my problem.
>>> In the SIESA-list I have not found how to optimize with BSE, can
>>> someone help me?
>>> Thanks in advance
>>>
>>> Gregorio
>>
>
--
-------------------------------------------------
Dr. Ricardo Faccio
Prof. Adjunto de Física
Mail: Cryssmat-Lab., Cátedra de Física, DETEMA
Facultad de Química, Universidad de la República
Av. Gral. Flores 2124, C.C. 1157
C.P. 11800, Montevideo, Uruguay.
E-mail: rfac...@fq.edu.uy
Phone: 598 2 924 98 59
598 2 929 06 48
Fax: 598 2 9241906
Web: http://cryssmat.fq.edu.uy/ricardo/ricardo.htm
