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<div class="moz-cite-prefix">Many thanks to Emine and Paolo for
correcting me.<br>
I was under the impression that DFT could handle only a few
hundred atoms.<br>
It seems I am mistaken. I hope to try to run one of these large
systems in the future<br>
<pre class="moz-signature" cols="72">Laalitha Liyanage
Department of Physics
Central Michigan University
Department of Physics
University of North Texas</pre>
On 04/25/2013 03:57 PM, Kucukbenli Emine wrote:<br>
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<div style="direction: ltr;font-family: Tahoma;color:
#000000;font-size: 10pt;">Dear Milinda, Laalitha<br>
<br>
This question actually belongs to pw_forum mailing list
(subscribe here : <a moz-do-not-send="true"
href="http://pwscf.org/mailman/listinfo/pw_forum"
target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a> )
<div><br>
Let me answer from experience,<br>
Some years ago I have run calculations on a system of >1000
atoms of C H O N atoms (cholesterol molecular crystal)</div>
<div>from as little as 128 to as many as 1024 processors on an
IBM SP6 machine and also on a Linux cluster.</div>
<div><br>
</div>
<div>I never had any problems with memory while running an
optimization calculation, I dont think it ever exceeded 1.5Gb
per processor. </div>
<div><br>
</div>
<div>I have just checked one of these calculations for you, 176
processors, the code prints as the largest occupied per
processor dynamical memory as 961 Mb. </div>
<div><br>
</div>
<div>Note that back then we didnt have band parallelization.</div>
<div>I was also running my calculations with a very high plane
wave cutoff for increased accuracy (required for NMR
calculations I wanted to run afterwards) meaning that you can
probably get away with less if you only want to optimize
atomic positions.</div>
<div><br>
</div>
<div>Of course you can always use a less accurate but cheaper
code first and fine tune your findings with Quantum Espresso
later, but I found it was not necessary in my case, starting
from experimental positions were enough. </div>
<div><br>
</div>
<div>best,</div>
<div>emine kucukbenli, postdoc at theos, epfl, switzerland</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
________________________________________<br>
From: <a class="moz-txt-link-abbreviated" href="mailto:q-e-developers-bounces@qe-forge.org">q-e-developers-bounces@qe-forge.org</a>
[<a class="moz-txt-link-abbreviated" href="mailto:q-e-developers-bounces@qe-forge.org">q-e-developers-bounces@qe-forge.org</a>] on behalf of Laalitha
Liyanage [<a class="moz-txt-link-abbreviated" href="mailto:laalitha.liyanage@unt.edu">laalitha.liyanage@unt.edu</a>]<br>
Sent: Thursday, April 25, 2013 10:14 PM<br>
To: Milinda Samaraweera; General discussion list for Quantum
ESPRESSO developers<br>
Subject: Re: [Q-e-developers] system size<br>
<br>
Dear Milinda,<br>
<br>
792 atom system is too large for Quantum Espresso.<br>
You can try to use SIESTA <a class="moz-txt-link-freetext" href="http://icmab.cat/leem/siesta/">http://icmab.cat/leem/siesta/</a><br>
<br>
Laalitha Liyanage<br>
Department of Physics<br>
Central Michigan University<br>
Department of Physics<br>
University of North Texas<br>
<br>
On 04/25/2013 01:01 PM, Milinda Samaraweera wrote:<br>
> Milinda Samaraweera<br>
> Computational materials chemistry and Computer
programming<br>
> University of Connecticut<br>
<br>
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