[Pw_forum] on the way of approximating a large slab

[Guido Fratesi]

Dear Yavar,

I hope a comment on your question (unfortunately not an answer) could be 
helpful.
Notice that the properties of the adsorbed species may converge faster 
than those of the clean surface alone. So, if you are interested in the 
distance of the molecule from the surface, or the adsorption energy, 
these may be described with a thin slab better than the interlayer 
relaxation or the surface energy of the clean substrate (or even worse, 
the surface electronic structure). You could practice by adsorbing a 
smaller molecule or a fragment. I'd expect that much less than 14 layers 
could be sufficient rather often.

(then, I remember about an "Effective Screening Medium Method" 
implemented in QE, there's also an example, but I don't know much about it)

HTH
Guido

Il 04/19/2012 11:57 AM, Yavar Taghipour Azar ha scritto:
> Dear QE users
>
> I want to model adsorption of a large molecule on a relatively large
> slab. After test convergence on the number of layers for clean surface,
> I found 14 layers are needed, but for well-known technical reasons (time
> and memory limitation), I am thinking on how can one take into account
> the atoms of just some 3 topmost layers of the slab, and the effects of
> the remaining layers of the slab as an external potential.
>
> Is it a meaningful question and what about its feasibility in the
> context of QE?
>
> Thanks in advance.
>
> -------------------------------------------
> Yavar Taghipour
> PhD Student
> Physics Group, AEOI
> Tehran-Iran
> Email: ytaghipour at aeoi.org.ir <mailto:ytaghipour at aeoi.org.ir>
> Phone: +98 (0) 21 82064556
> -----------------------------------------------------------
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum

-- 
Guido Fratesi

Dipartimento di Scienza dei Materiali
Universita` degli Studi di Milano-Bicocca
via Cozzi 53, 20125 Milano, Italy