Mehmet, No hurries, take your time... Unless you really wish to :)
Marcos On Wed, Jul 28, 2010 at 9:17 PM, Mehmet Topsakal < topsa...@unam.bilkent.edu.tr> wrote: > OK. I will try to prepare a detailed SIESTA-PHON tutorial at this weekend. > > > > 2010/7/28 Marcos Veríssimo Alves <marcos.verissimo.al...@gmail.com> > > Mehmet, >> >> Please do share the knowledge. It is alwayfs useful, especislly because >> the calculation of phonons is always of interest. I for one would be very >> much interested in knowing how to use Dario's code in conjunction with >> Siesta. >> >> Cheers, >> >> Marcos >> >> On Wed, Jul 28, 2010 at 1:43 PM, Mehmet Topsakal < >> topsa...@unam.bilkent.edu.tr> wrote: >> >>> Dear Jusar, >>> >>> I have obtained the attached phonon spectrum in 2 hours by using >>> 8-cpu-core. The supercell is 5x5x1 and the MeshCutoff is 300 Ry. I have used >>> Dario Alfè's phon program. Because I'm not familiar with siesta utilities >>> such as FCBUILD and VIBRA. Phon only needs forces which can be calculated by >>> other programs such as VASP and PWSCF. >>> >>> I can prepare a nice and detaied phon tutorial where the forces are >>> calculated by SIESTA if you (or others) want. >>> >>> Mehmet. >>> >>> >>> >>> On Wed, Jul 28, 2010 at 11:46 AM, Juzar Thingna <juza...@gmail.com>wrote: >>> >>>> Thank you Prof. Postnikov and Mehmet for your quick responses. Here are >>>> a few observations. >>>> >>>> After Mehmets comment on increasing the Mesh cut-off I set it to 800 Ry >>>> I still observed negative part but the magnitude has reduced. Sorry I >>>> didn't >>>> know one had to go to such high cut-offs to observe a change, earlier I was >>>> trying cut-offs from 200-500 and there were no changes (or maybe changes >>>> that were not very distinguishable). >>>> >>>> I'm currently trying Prof. Postnikov solution of increasing the >>>> super-cell size. Now I have set SuperCell_1 = 5; SuperCell_1 = 5; >>>> SuperCell_1 = 1. Increasing the supercell size has drastically increased >>>> the >>>> computation time (as expected) so I guess it will take a long time to get >>>> over. >>>> >>>> Is there a way to increase the SuperCell size but not affect the >>>> computation time drastically? >>>> >>>> >>>> Regards, >>>> >>>> Juzar Thingna >>>> Department of Physics, >>>> Center for Computation Science and Engineering, >>>> National University of Singapore. >>>> >>>> >>>> On Tue, Jul 27, 2010 at 5:42 PM, <apost...@uni-osnabrueck.de> wrote: >>>> >>>>> > Hi, >>>>> > Thank you Prof. Postnikov and Mehmet for your quick replies. >>>>> > >>>>> > I do get 3 acoustic modes and 3 optical modes as I should since I >>>>> just >>>>> > have >>>>> > a 2 point basis. >>>>> > The problem is that one of the acoustic mode starts from zero and >>>>> goes >>>>> > negative immediately (Graph attached). I have tried increasing the >>>>> mesh >>>>> > cut-off as well as optimized the structure using CG. But still I get >>>>> the >>>>> > same behavior. >>>>> >>>>> Dear Juzar, >>>>> then it is clear. (You should have described your problem >>>>> more precisely in the first place, to save some guess work). >>>>> The trouble is due to >>>>> insufficient supercell size in your VIBRA calculation. >>>>> In other words, the force constants >>>>> are not sufficiently converged in real space. You need to construct >>>>> a larger supercell, using FCBUILD, then rerun VIBRA. >>>>> >>>>> > @ Prof. Postnikov: Sir you mentioned "Go search for a better >>>>> equilibrium. >>>>> > Use eigenvectors of instable modes as a guide." Please could you >>>>> elaborate >>>>> > on how to use the eigen vectors of the instable mode as a guide? >>>>> >>>>> Seemingly, this is not your problem here. >>>>> However, you may have a look in the following talk >>>>> >>>>> http://www.home.uni-osnabrueck.de/apostnik/Lectures/APostnikov-Phonons.pdf >>>>> - your problem is addressed in pp.18-20. >>>>> >>>>> Good luck >>>>> >>>>> Andrei Postnikov >>>>> >>>>> >>>>> >>>> >>> >>> >>> -- >>> >>> Mehmet Topsakal (Ph.D. Student) >>> UNAM-Institute of Materials Science and Nanotechnology. >>> Bilkent University. 06800 Bilkent, Ankara/Türkiye >>> Tel: 0090 312 290 3527 ; Fax: 0090 312 266 4365 >>> UNAM-web : www.nano.org.tr >>> >>> >> > > > -- > > Mehmet Topsakal (Ph.D. Student) > UNAM-Institute of Materials Science and Nanotechnology. > Bilkent University. 06800 Bilkent, Ankara/Türkiye > Tel: 0090 312 290 3527 ; Fax: 0090 312 266 4365 > UNAM-web : www.nano.org.tr > >
