Axel,<br><br>Thanks for the advice. I take your point and agree that my results would be much more meaningful with a better knowledge base. Hopefully I won't have any more questions until I can ask one worth asking. My initial goal was to see whether finding Raman phonon intensities on a system this size was feasible with the resources I have available and I think I've answered that question.<br>
<br>It's definitely a testament to the software that a spectroscopist with no plane-wave experience could get the software "working" in just 3 days. I guess with ease comes black-box users. <br><br>Thanks for your help,<br>
<br>Matt<br><br><div class="gmail_quote">On Thu, May 3, 2012 at 1:01 AM, Axel Kohlmeyer <span dir="ltr"><<a href="mailto:akohlmey@gmail.com" target="_blank">akohlmey@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On Tue, May 1, 2012 at 11:33 PM, matt reish <<a href="mailto:reishme04@gmail.com">reishme04@gmail.com</a>> wrote:<br>
<br>
matt,<br>
<div class="im"><br>
> Thanks for the reply, seemed to be going way too fast for what I had read I<br>
> that I should expect. Any thoughts on what would be more reasonable cutoffs<br>
> for wavefunction and density? Would it be reasonable to try to attain a<br>
> useable result on a "cluster" using 8 processors?<br>
<br>
</div>it is not the computational resources that you should worry about,<br>
but the fact that you are trying to use a tool without knowing how<br>
its fundamental principles work. quantum espresso has great<br>
tutorials and there are several good textbooks and papers<br>
to work through. working with plane waves and pseudopotentials<br>
is not overly difficult, but using them without knowing what you<br>
are doing, is like waving around a loaded sawn-off shotgun.<br>
<br>
simulation software is brutal: it will often run smoothly and<br>
produce "numbers", even if you feed it complete nonsense.<br>
<br>
cheers,<br>
axel.<br>
<div class="HOEnZb"><div class="h5"><br>
><br>
> Cheers,<br>
><br>
> Matt<br>
><br>
><br>
> On Wed, May 2, 2012 at 3:02 PM, Axel Kohlmeyer <<a href="mailto:akohlmey@gmail.com">akohlmey@gmail.com</a>> wrote:<br>
>><br>
>> On Tue, May 1, 2012 at 10:53 PM, matt reish <<a href="mailto:reishme04@gmail.com">reishme04@gmail.com</a>> wrote:<br>
>> > Hi PW list,<br>
>> ><br>
>> > I am working with Quantum Espresso (v4.3.2.1) in the hopes of attaining<br>
>> > Raman phonon frequencies of a benzoic acid crystal. I attained the<br>
>> > optimized<br>
>> > output geometry from a CASTEP calculation in the supplemental material<br>
>> > of a<br>
>> > paper. This geometry was used by the authors to calculate accurate IR<br>
>> > phonon<br>
>> > frequencies. I used a 'relax' calculation in Quantum Espresso on the<br>
>> > optimized geometry but this led to large shifts in the atomic positions<br>
>> > in<br>
>> > the lattice and unreasonable structures for the molecules in the lattice<br>
>> > after finding the optimized structure. My question is does anyone have a<br>
>> > some experience calculating organic crystals in Quantum Espresso that<br>
>> > could<br>
>> > give me some tips?<br>
>><br>
>><br>
>> matt,<br>
>><br>
>> you are using a *ridiculously* low wavefunction<br>
>> and density cutoff, that means your basis set<br>
>> is *far* too small. unphysical results are the<br>
>> logical consequence.<br>
>><br>
>> axel.<br>
>><br>
>><br>
>> ><br>
>> > Here is my input file minus the atomic posititions:<br>
>> ><br>
>> > &CONTROL<br>
>> > title = 'benzacidscftest' ,<br>
>> > calculation = 'relax' ,<br>
>> > restart_mode = 'from_scratch' ,<br>
>> > outdir = '/home/mreish/tmp/' ,<br>
>> > pseudo_dir = '/usr/share/espresso/pseudo/' ,<br>
>> > prefix = 'batest5' ,<br>
>> > disk_io = 'default' ,<br>
>> > nstep = 600 ,<br>
>> > /<br>
>> > &SYSTEM<br>
>> > ibrav = 12,<br>
>> > A = 5.4996 ,<br>
>> > B = 5.1283 ,<br>
>> > C = 21.950 ,<br>
>> > cosAB = 0 ,<br>
>> > cosAC = -.128276341 ,<br>
>> > cosBC = 0 ,<br>
>> > nat = 60,<br>
>> > ntyp = 3,<br>
>> > ecutwfc = 5 ,<br>
>> > ecutrho = 40 ,<br>
>> > /<br>
>> > &ELECTRONS<br>
>> > electron_maxstep = 200,<br>
>> > conv_thr = 1.0d-11 ,<br>
>> > /<br>
>> > &IONS<br>
>> > /<br>
>> > ATOMIC_SPECIES<br>
>> > C 12.01000 C.pbe-rrkjus.UPF<br>
>> > O 16.00000 O.pbe-rrkjus.UPF<br>
>> > H 1.00000 H.pbe-rrkjus.UPF<br>
>> > ATOMIC_POSITIONS angstrom<br>
>> ><br>
>> > K_POINTS automatic<br>
>> > 1 1 1 1 1 1<br>
>> ><br>
>> ><br>
>> > Cheers,<br>
>> ><br>
>> > Matthew Reish<br>
>> > University of Otago<br>
>> > Dunedin<br>
>> > New Zealand<br>
>> ><br>
>> > _______________________________________________<br>
>> > Pw_forum mailing list<br>
>> > <a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
>> > <a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br>
>> ><br>
>><br>
>><br>
>><br>
>> --<br>
>> Dr. Axel Kohlmeyer<br>
>> <a href="mailto:akohlmey@gmail.com">akohlmey@gmail.com</a> <a href="http://goo.gl/1wk0" target="_blank">http://goo.gl/1wk0</a><br>
>><br>
>> College of Science and Technology<br>
>> Temple University, Philadelphia PA, USA.<br>
><br>
><br>
<br>
<br>
<br>
--<br>
Dr. Axel Kohlmeyer<br>
<a href="mailto:akohlmey@gmail.com">akohlmey@gmail.com</a> <a href="http://goo.gl/1wk0" target="_blank">http://goo.gl/1wk0</a><br>
<br>
College of Science and Technology<br>
Temple University, Philadelphia PA, USA.<br>
</div></div></blockquote></div><br>