[Pw_forum] on the way of approximating a large slab

[Yavar Taghipour Azar]

Dear Guido,

Thanks for your consideration and very instructive comments.



Bests.
-------------------------------------------
Yavar Taghipour
PhD Student
Physics Group, AEOI
Tehran-Iran

Email: ytaghipour at aeoi.org.ir
Phone: +98 (0) 21 82064556
-----------------------------------------------------------
----- Original Message ----- 
From: "Guido Fratesi" <fratesi at mater.unimib.it>
To: <pw_forum at pwscf.org>
Sent: Thursday, April 19, 2012 2:55 PM
Subject: Re: [Pw_forum] on the way of approximating a large slab


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