Axel, 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.
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. Thanks for your help, Matt On Thu, May 3, 2012 at 1:01 AM, Axel Kohlmeyer <akohlmey at gmail.com> wrote: > On Tue, May 1, 2012 at 11:33 PM, matt reish <reishme04 at gmail.com> wrote: > > matt, > > > Thanks for the reply, seemed to be going way too fast for what I had > read I > > that I should expect. Any thoughts on what would be more reasonable > cutoffs > > for wavefunction and density? Would it be reasonable to try to attain a > > useable result on a "cluster" using 8 processors? > > it is not the computational resources that you should worry about, > but the fact that you are trying to use a tool without knowing how > its fundamental principles work. quantum espresso has great > tutorials and there are several good textbooks and papers > to work through. working with plane waves and pseudopotentials > is not overly difficult, but using them without knowing what you > are doing, is like waving around a loaded sawn-off shotgun. > > simulation software is brutal: it will often run smoothly and > produce "numbers", even if you feed it complete nonsense. > > cheers, > axel. > > > > > Cheers, > > > > Matt > > > > > > On Wed, May 2, 2012 at 3:02 PM, Axel Kohlmeyer <akohlmey at gmail.com> > wrote: > >> > >> On Tue, May 1, 2012 at 10:53 PM, matt reish <reishme04 at gmail.com> > wrote: > >> > Hi PW list, > >> > > >> > I am working with Quantum Espresso (v4.3.2.1) in the hopes of > attaining > >> > Raman phonon frequencies of a benzoic acid crystal. I attained the > >> > optimized > >> > output geometry from a CASTEP calculation in the supplemental material > >> > of a > >> > paper. This geometry was used by the authors to calculate accurate IR > >> > phonon > >> > frequencies. I used a 'relax' calculation in Quantum Espresso on the > >> > optimized geometry but this led to large shifts in the atomic > positions > >> > in > >> > the lattice and unreasonable structures for the molecules in the > lattice > >> > after finding the optimized structure. My question is does anyone > have a > >> > some experience calculating organic crystals in Quantum Espresso that > >> > could > >> > give me some tips? > >> > >> > >> matt, > >> > >> you are using a *ridiculously* low wavefunction > >> and density cutoff, that means your basis set > >> is *far* too small. unphysical results are the > >> logical consequence. > >> > >> axel. > >> > >> > >> > > >> > Here is my input file minus the atomic posititions: > >> > > >> > &CONTROL > >> > title = 'benzacidscftest' , > >> > calculation = 'relax' , > >> > restart_mode = 'from_scratch' , > >> > outdir = '/home/mreish/tmp/' , > >> > pseudo_dir = '/usr/share/espresso/pseudo/' , > >> > prefix = 'batest5' , > >> > disk_io = 'default' , > >> > nstep = 600 , > >> > / > >> > &SYSTEM > >> > ibrav = 12, > >> > A = 5.4996 , > >> > B = 5.1283 , > >> > C = 21.950 , > >> > cosAB = 0 , > >> > cosAC = -.128276341 , > >> > cosBC = 0 , > >> > nat = 60, > >> > ntyp = 3, > >> > ecutwfc = 5 , > >> > ecutrho = 40 , > >> > / > >> > &ELECTRONS > >> > electron_maxstep = 200, > >> > conv_thr = 1.0d-11 , > >> > / > >> > &IONS > >> > / > >> > ATOMIC_SPECIES > >> > C 12.01000 C.pbe-rrkjus.UPF > >> > O 16.00000 O.pbe-rrkjus.UPF > >> > H 1.00000 H.pbe-rrkjus.UPF > >> > ATOMIC_POSITIONS angstrom > >> > > >> > K_POINTS automatic > >> > 1 1 1 1 1 1 > >> > > >> > > >> > Cheers, > >> > > >> > Matthew Reish > >> > University of Otago > >> > Dunedin > >> > New Zealand > >> > > >> > _______________________________________________ > >> > Pw_forum mailing list > >> > Pw_forum at pwscf.org > >> > http://www.democritos.it/mailman/listinfo/pw_forum > >> > > >> > >> > >> > >> -- > >> Dr. Axel Kohlmeyer > >> akohlmey at gmail.com http://goo.gl/1wk0 > >> > >> College of Science and Technology > >> Temple University, Philadelphia PA, USA. > > > > > > > > -- > Dr. Axel Kohlmeyer > akohlmey at gmail.com http://goo.gl/1wk0 > > College of Science and Technology > Temple University, Philadelphia PA, USA. > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20120503/40e7414c/attachment.htm
