Dear Prof. Isaev, Thank you very much for your detailed answer. It is clear for me now.
MyTrinh > > Hi, > > --- On Thu, 10/8/09, vtmtrinh at caltech.edu <vtmtrinh at caltech.edu> wrote: > >> My main purpose is to calculate the phonon dispersion curve from Gamma >> to X for Si. I'd like to reproduce the Si phonon dispersion curve from >> > Gamma to X.? > > In order to do this one correctly first you should calculate dynamical > matrices for a given q-mesh, then perform FFT by q2r.x, then apply > matdyn.x to calculate phonons along given directions (specifying a list > of q-points). In this way you apply ASR for both q2r.x and matdyn.x > calculations. > > If you have only \Gamma-point phonons you can use dynmat.x to apply ASR. > >> I thought that after the scf calculation for 10x10x10, I can >> run phonon calculation directly for a series of q points from Gamma to >> X (let say 5 points).? Then from there, I use q2r.x and then >> dynmat.x to calculate intermediate points in order to fix the non-zero >> > frequency at Gamma point (applying ASR) and to get a smooth >> dispersion > curve curve.? > > This is a wrong way to calculate phonons. Of course, you can calculate > phonons for any q-point you like, but they are not oblidged to form a > proper mesh for Fast-Fourier-Transformation. In this way you always will > meet troubles with q2r.x (FFT). > >> However, the phonon calculation (the first crash) crashed all the >> >times.? Now I am testing by running phonon calculation for a mesh of >> >4x4x4 to see if it still crashes. If it works, this means that direct >> calculation of phonon by specifying directly q points along G-X does >> not >> work.? However, this will be expensive calculation if to get phonon >> dispersion a long one direction, I have to do the 3D-messh phonon >> calculation first. >> >> If I did only a single q-point calculation one at a time, >> which would be much faster than does the approach above, > > Sorry, I am not sure I exactly understand what you mean, but calculations > performed in the right way (see above) give you Interatomic Force > Constants (IFC) matrix which allows you to evaluate many thermodynamical > properties, besides phonons along high symmetry directions. > >>how could I specify q-grid in q2r.x? > > You should not specify q-grid in q2r.x's input file. It (q2r.x) reads > Sysname.dyn0 file generated by ph.x which contains info about the q-grid > (divisions along each basis vectors, total number of q-points and q-points > itself. > > Of course, you could calculate dynamical matrices in the old manner, > specifying a list of q-points (but they have to be a result of KxLxM mesh, > and calculated before you start phonon calculations). In this case you can > follow your example given below. > >> >> Also, I have another question, if I would like to apply ASR >> to fix the phonon freq. at Gamma point, is it correct to just specify >> the q-grid in the input files for q2r.x and matdyn.x as follows: >> >> &input >> ? ? fildyn='si.dyn', zasr='crystal', >> flfrc='si.fc' >> ? / >> 1 1 1 >> 1 >> si.dyn1? ? !this the *.dyn file at gamma > > I do not think so, as q2r.x calculates IFC Matrix, not phonon modes as > matdyn.x does this job. > How to apply ASR for Gamma-point phonons see above. > > Bests, > Eyvaz. > > ------------------------------------------------------------------- > Prof. Eyvaz Isaev, > Theoretical Physics Department, Moscow State Institute of Steel & Alloys, > Russia, > Department of Physics, Chemistry, and Biology (IFM), Linkoping University, > Sweden > Condensed Matter Theory Group, Uppsala University, Sweden > Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com > > __________________________________________________ > Do You Yahoo!? > Tired of spam? Yahoo! Mail has the best spam protection around > http://mail.yahoo.com > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >