<html dir="ltr">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style type="text/css" id="owaParaStyle"></style>
</head>
<body fpstyle="1" ocsi="0">
<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 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: q-e-developers-bounces@qe-forge.org [q-e-developers-bounces@qe-forge.org] on behalf of Laalitha Liyanage [laalitha.liyanage@unt.edu]<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 http://icmab.cat/leem/siesta/<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>
_______________________________________________<br>
Q-e-developers mailing list<br>
Q-e-developers@qe-forge.org<br>
http://qe-forge.org/mailman/listinfo/q-e-developers<br>
</div>
</div>
</body>
</html>