[Pw_forum] big calculations II

[Ricardo Faccio]

Dear Nicola
Thanks for the recommendations!
Regards
Ricardo

--------------------------------------------
Dr. Ricardo Faccio
Prof. Adj. de Física

Av. Gral. Flores 2124. CC 1157. CP 11800.
Phone: + 598 2 924 9859
Fax: + 598 2 924 1906
Web: http://cryssmat.fq.edu.uy/ricardo/ricardo.htm
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El 20/01/2011, a las 08:19, Nicola Marzari <nicola.marzari at materials.ox.ac.uk 
 > escribió:

> On 1/20/11 2:26 AM, Ricardo Faccio wrote:
>> Dear nicola
>> Thanks gr your email, i would like to take the opportunity and ask  
>> you
>> a further question. I have a similar situation than José. I'm work 
>> ing
>> with a cobalt porphyrin deposited over a metallic substrate (similar
>> to your recent PRL). I optimized the structure with gamma point with
>> 25 and 250 ecut and rhocut respectively. It takes almost the 100% of
>> my 8Gb RAM quad core computer. Now i want to get a reasonably DOS fir
>> this system, but i need more k-points, and thus I will need more RAM
>> memory. Would you recommend anything else for getting a good DOS for
>> my quad core 8 GB RAM machine?
>> Thank you in advance.
>> Ricardo
>
>
> Dear Ricardo,
>
> two options, I think - the simplest is that a nscf calculation,
> dealing with one k-point at a time, would not really require more
> RAM, but for the fact that k-points different from gamma have
> complex wavefunctions (so indeed you might be out of luck).
>
> Another possibility would be to calculate the Wannier functions
> for this system, and then use Wannier interpolation (see our 2005
> PRL Lee et al.). This can work extremely well, but it requires  
> learning
> a new code.
>
> As a side note, the CP codes requires much less memory than PWSCF -
> it has only gamma sampling, though. It does deal with metals, using
> the "ensemble-DFT" approach, but that has not been optimized as much
> as the other parts. Worth trying, though!
>
> A last resort would be to decrease the thickness of your slab - (111)
> surfaces could be ok with as little as 3 layers, or maybe even 2  
> (maybe you could put a few more atoms in the 3rd layer below the  
> cobalt).
>
>            nicola
>
>
>
> -- 
> ----------------------------------------------------------------------
> Prof Nicola Marzari    Department of Materials    University of Oxford
> Chair of Materials Modelling  Director, Materials Modelling Laboratory
> nicola.marzari at materials.ox.ac.uk     http://mml.materials.ox.ac.uk/NM