Hi Ankit Jain, Germanium &inputph tr2_ph=1.0d-18 ldisp=.true. nq1=10 nq2=10 nq3=1 prefix='GEPH_dfpt' outdir='/scratch' fildyn='./dfpt_10x/ge.dyn' /
this activate a dispersive phonon calculation. If you switch the ldisp flag to .false. , if you unset nq1, nq2 and nq3 (you just neglect those) and if you specify q1 q2 and q3 at the very end of the input file (after the final slash /) you can calculate the frequencies at that q point. Ex. Germanium &inputph tr2_ph=1.0d-18 prefix='GEPH_dfpt' outdir='/scratch' fildyn='./dfpt_10x/ge.dyn' / 1.0 0.0 0.0 I suggest you to pick one q point where you found imaginary frequencies (from your frequencies output file) and just run ph.x < ph.in on it. However I have to tell you that I am not familiar with phonon calculation on surfaces which I believe it's what you are doing right now. Am I correct? i see that your cell is stretched along "z" and you k-sampling is highly non-homogeneous. This may dramatically effects your phonon calculation. One last thing...did you relax through a vc-relax job or is that a pseudo-crystal experimental structure? On Sun, Aug 31, 2014 at 7:28 PM, ankit jain <ankitjain.me.iitk at gmail.com> wrote: > Hello Vincenzo, > > Thanks a lot for your reply. > > > "First thing that i would try is to check if phonon calculations at a q > point where matdyn gives you negative is correct or not" > How would I check this? > > Also I am using tr2_ph = 1e-18 in the ph.in and conv_thr=1.0d-12 in the > pw.in file. > My kgrid is 14*12*1 in the pw.in file. > > Thanks, > Ankit Jain > > > > On Sun, Aug 31, 2014 at 1:13 PM, Vincenzo Verdolino < > vincenzo.verdolino at gmail.com> wrote: > >> Dear, >> >> I have similar issues so i am not sure to be able to help you. First >> thing that i would try is to check if phonon calculations at a q point >> where matdyn gives you negative is correct or not. If yes that means that >> you k-samplin is good enough and it is only a matter of q mash for the FFT. >> Another check should be on the scf thrashold in ph.in input file >> >> >> Let me know >> >> Sent from my iPhone >> >> > On 31/ago/2014, at 17:03, ankit jain <ankitjain.me.iitk at gmail.com> >> wrote: >> > >> > >> > Hello QE developers and users, >> > >> > Recently, I am trying to calculate phonon dispersion of a 2D material >> using pw.x, ph.x, q2r.x and matdyn.x but I am getting very strange results. >> > >> > In my calculations the phonon frequencies reported by ph.x are all real >> for all non-gamma phonon q-points. But, when I use matdyn.x to calculate >> phonon frequencies at other points (other than the one for which ph.x >> calculated frequencies), I get negative (imaginary) frequencies. And these >> negative frequencies are present for non-gamma points as can be seen in >> attached frequency file. >> > >> > I am having difficulty in understanding these results and hoping >> someone could help. >> > >> > Thank You, >> > Ankit Jain >> > PhD Candidate >> > IIT India >> > >> > <pw.in> >> > <ph.in> >> > <q2r.in> >> > <matdyn.in> >> > <frequency> >> > _______________________________________________ >> > Pw_forum mailing list >> > Pw_forum at pwscf.org >> > http://pwscf.org/mailman/listinfo/pw_forum >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140831/3a3b2fab/attachment.html
