[Pw_forum] Strange phonon branches appear in phonon dispersion
> > Dear Dr. Stefano and Dr. Mohr, Thank you for your comments, Actually I had successfully done phonon dispersion and EPC for Al bulk structure with good results so from now I want to apply for the Al wires structures. Firstly I calculate for 2 atom cell of Al with zigzag wires, and I got 6 phonon modes along q-points and appear some negative frequencies, so I tried to improve my calculation but always appear negative acoustic frequencies (optical branch is no problem) and then I did with 4, 6 atom cell and of course I got 3-n modes but my results still no good like I expect. :( To check my set up parameters I calculate the same procedure for Al 1D linear chain with 1 and 2 atom cell with hopefully the phonon curves will be the same as I studied theoretically in Solid States books, but it was not :(. So should my calculation be wrong with this system. Could you give me advice about my input parameters? Please keep your eyes my INPUT files (in case of 2 atoms in zigzag chain) Al.scf.fit.in &SYSTEM ibrav = 6, celldm(1) = 39.994, celldm(3) = 0.199762906, nat = 2, ntyp = 1, ecutwfc = 25.D0 , ecutrho = 300, occupations = 'smearing' , degauss = 0.05 , smearing = 'methfessel-paxton' , la2F = .true. / &ELECTRONS conv_thr = 1.D-10 , mixing_beta = 0.7D0 , / ATOMIC_SPECIES Al 26.98000 Al.vbc.UPF ATOMIC_POSITIONS angstrom Al 0.0 1.517315647 2.138739361 Al 0.0 0.116702849 0.023699809 K_POINTS automatic 4 4 40 0 0 0 Al.scf.in &SYSTEM ibrav = 6, celldm(1) = 39.994, celldm(3) = 0.199762906, nat = 2, ntyp = 1, ecutwfc = 25.D0 , ecutrho = 300, occupations = 'smearing' , degauss = 0.05 , smearing = 'methfessel-paxton' / &ELECTRONS conv_thr = 1.D-10 , mixing_beta = 0.7D0 , / ATOMIC_SPECIES Al 26.98000 Al.vbc.UPF ATOMIC_POSITIONS angstrom Al 0.0 1.517315647 2.138739361 Al 0.0 0.116702849 0.023699809 K_POINTS automatic 2 2 20 0 0 0 Al.elph.in Electron-phonon coefficients for Alwire_2 &inputph tr2_ph=1.0d-14, prefix='al2_elph', fildvscf='al2d', filelph='matrix' amass(1)=26.98, outdir='/root/tmp/', fildyn='al2m.dyn', elph=.true., trans=.true., ldisp=.true. nq1=1, nq2=1, nq3=10, And hereafter 6 modes I got &plot nbnd= 6, nks= 27 / 0.00 0.00 0.00 -0.0855 -0.04500. 20.7938 196.2309 372.4942 0.00 0.00 0.10 -13.14325.66575.7114 20.3098 196.7060 372.0899 0.00 0.00 0.20 -25.6753 10.2550 10.5805 18.8468 198.1533 371.0008 0.00 0.00 0.30 -37.6999 14.0728 14.1858 16.2544 200.5950 369.4869 0.00 0.00 0.40 -48.8295 11.6034 16.4265 16.4576 203.9728 367.7201 0.00 0.00 0.50 -58.7192 -5.6944 16.7453 17.6129 208.1190 365.6663 0.00 0.00 0.60 -67.0895 -15.3952 14.9673 18.4203 212.8051 363.1793 0.00 0.00 0.70 -73.7443 -21.7038 11.9605 19.3942 217.8126 360.1938 0.00 0.00 0.80 -78.6120 -26.99489.8326 20.4642 222.9635 356.8134 0.00 0.00 0.90 -81.7857 -31.7595 10.1665 21.2176 228.1041 353.2106 0.00 0.00 1.00 -83.4878 -36.1149 10.5785 21.4924 233.0809 349.4591 0.00 0.00 1.10 -83.9637 -39.93806.4409 21.5912 237.7521 345.4939 0.00 0.00 1.20 -83.3549 -43.0700 -11.8614 21.8643 242.0400 341.2345 0.00 0.00 1.30 -81.7148 -45.5109 -19.5363 22.1233 245.9755 336.7214 0.00 0.00 1.40 -79.2450 -47.4002 -24.2602 21.7049 249.6731 332.1110 0.00 0.00 1.50 -76.4698 -48.7989 -26.8527 20.1426 253.2412 327.5276 0.00 0.00 1.60 -74.0708 -49.5494 -28.8342 17.6459 256.7020 322.9460 0.00 0.00 1.70 -72.4259 -49.4368 -31.6947 14.8469 259.9856 318.2672 0.00 0.00 1.80 -71.2114 -48.4948 -35.6608 11.6256 263.0044 313.5063 0.00 0.00 1.90 -69.6799 -47.0750 -39.79634.2536 265.7429 308.8670 0.00 0.00 2.00 -67.4586 -45.5010 -43.2503 -12.7026 268.2849 304.5960 0.00 0.00 2.10 -64.9647
[Pw_forum] Strange phonon branches appear in phonon dispersion
>> >> Dear Dr. Stefano and Dr. Mohr, ^^ That is too much honour for me as I am still working on these two letters. The input below looks ok for me, but two things: 1.) for electronic wavefunctions you choose a 4 4 40 grid. It should be no difference to a 1 1 40 one (because of 1 dim, there are no bloch waves perp to your wire axis) 2.) your tr2_ph=1.0d-14 is maybe too small. try to use a value around 1.0d-20 What about the convergence of the other parameters (ecutwfc) with respect to your phonon frequencies? Maybe you find some information in the paper verstraete PhysRevB 74 153408 (2006). Best Marcel > > > Thank you for your comments, > > Actually I had successfully done phonon dispersion and EPC for Al bulk > structure with good results so from now I want to apply for the Al wires > structures. Firstly I calculate for 2 atom cell of Al with zigzag wires, and > I got 6 phonon modes along q-points and appear some negative frequencies, so > I tried to improve my calculation but always appear negative acoustic > frequencies (optical branch is no problem) and then I did with 4, 6 atom > cell and of course I got 3-n modes but my results still no good like I > expect. :( > To check my set up parameters I calculate the same procedure for Al 1D > linear chain with 1 and 2 atom cell with hopefully the phonon curves will be > the same as I studied theoretically in Solid States books, but it was not > :(. So should my calculation be wrong with this system. Could you give me > advice about my input parameters? Please keep your eyes my INPUT files (in > case of 2 atoms in zigzag chain) > > Al.scf.fit.in > > &SYSTEM > ibrav = 6, > celldm(1) = 39.994, > celldm(3) = 0.199762906, > nat = 2, >ntyp = 1, > ecutwfc = 25.D0 , > ecutrho = 300, > occupations = 'smearing' , > degauss = 0.05 , >smearing = 'methfessel-paxton' , > la2F = .true. > / > &ELECTRONS >conv_thr = 1.D-10 , > mixing_beta = 0.7D0 , > / > ATOMIC_SPECIES > Al 26.98000 Al.vbc.UPF > ATOMIC_POSITIONS angstrom > Al 0.0 1.517315647 2.138739361 > Al 0.0 0.116702849 0.023699809 > K_POINTS automatic > 4 4 40 0 0 0 > > Al.scf.in > > &SYSTEM > ibrav = 6, > celldm(1) = 39.994, > celldm(3) = 0.199762906, > nat = 2, >ntyp = 1, > ecutwfc = 25.D0 , > ecutrho = 300, > occupations = 'smearing' , > degauss = 0.05 , >smearing = 'methfessel-paxton' > / > &ELECTRONS >conv_thr = 1.D-10 , > mixing_beta = 0.7D0 , > / > ATOMIC_SPECIES > Al 26.98000 Al.vbc.UPF > ATOMIC_POSITIONS angstrom > Al 0.0 1.517315647 2.138739361 > Al 0.0 0.116702849 0.023699809 > K_POINTS automatic > 2 2 20 0 0 0 > > Al.elph.in > > Electron-phonon coefficients for Alwire_2 > &inputph > tr2_ph=1.0d-14, > prefix='al2_elph', > fildvscf='al2d', > filelph='matrix' > amass(1)=26.98, > outdir='/root/tmp/', > fildyn='al2m.dyn', > elph=.true., > trans=.true., > ldisp=.true. > nq1=1, nq2=1, nq3=10, > > And hereafter 6 modes I got > > &plot nbnd= 6, nks= 27 / >0.00 0.00 0.00 > -0.0855 -0.04500. 20.7938 196.2309 372.4942 >0.00 0.00 0.10 > -13.14325.66575.7114 20.3098 196.7060 372.0899 >0.00 0.00 0.20 > -25.6753 10.2550 10.5805 18.8468 198.1533 371.0008 >0.00 0.00 0.30 > -37.6999 14.0728 14.1858 16.2544 200.5950 369.4869 >0.00 0.00 0.40 > -48.8295 11.6034 16.4265 16.4576 203.9728 367.7201 >0.00 0.00 0.50 > -58.7192 -5.6944 16.7453 17.6129 208.1190 365.6663 >0.00 0.00 0.60 > -67.0895 -15.3952 14.9673 18.4203 212.8051 363.1793 >0.00 0.00 0.70 > -73.7443 -21.7038 11.9605 19.3942 217.8126 360.1938 >0.00 0.00 0.80 > -78.6120 -26.99489.8326 20.4642 222.9635 356.8134 >0.00 0.00 0.90 > -81.7857 -31.7595 10.1665 21.2176 228.1041 353.2106 >0.00 0.00 1.00 > -83.4878 -36.1149 10.5785 21.4924 233.0809 349.4591 >0.00 0.00 1.10 > -83.9637 -39.93806.4409 21.5912 237.7521 345.4939 >0.00 0.00 1.20 > -83.3549 -43.0700 -11.8614 21.8643 242.0400 341.2345 >0.00 0.00 1.30 > -81.7148 -45.5109 -19.5363 22.1233 245.9755 336.7214 >
[Pw_forum] Strange phonon branches appear in phonon dispersion
Dear Pw_users, I am trying to do calculation phonon dispersion and EPC for 1D Aluminum chain. I got the results which are strange phonon branches appearing. In the case of 2 atom-cell, I got 4 phonon branches, two of them are Optical and Acoustical phonon branches and two others, which have zero and negative values, are unknown for me. In the case if I have 1 atom-cell, that strange branch also appears. Could any body explain for me what kind of frequencies here? I was surfing this forum and FAQ and I found many discussion about negative frequencies, but I still cannot find the answers for me. Bac This is my relaxed unitcell For 1-atom cell input alat = 20. (a.u.) CELL_PARAMETERS (alat) 0.999558675 0.0 0.0 0.0 0.999558675 0.0 0.0 0.0 0.224680571 ATOMIC_POSITIONS (angstrom) Al 0.0 0.0 0.0 For 2-atom cell CELL_PARAMETERS (alat) 1.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.45330 ATOMIC_POSITIONS (angstrom) Al 0.0 0.0 2.39900 Al 0.0 0.0 0.0 And INPUT for ph.x tr2_ph=1.0d-12, prefix='al_20', fildvscf='Al2v', amass(1)=26.98, outdir='/root/tmp/', fildyn='al2.dyn', elph=.true., trans=.true., ldisp=.true. nq1=1, nq2=1, nq3=10 -- Phung Viet Bac Division of Mathematical and Physical Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, JAPAN -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20071212/dc68af2d/attachment.htm
[Pw_forum] Strange phonon branches appear in phonon dispersion
>> I am trying to do calculation phonon dispersion and EPC for 1D >> Aluminum chain. I got the results which are strange phonon branches >> appearing. In the case of 2 atom-cell, I got 4 phonon branches, two of >> them are Optical and Acoustical phonon branches and two others, which >> have zero and negative values, are unknown for me. In the case if I >> have 1 atom-cell, that strange branch also appears. Could any body >> explain for me what kind of frequencies here? 6 branches for 2 atom are what one expects (in general 3n branches and 3 acoustical and 3n-3 optical ones). However negative values indicate some error in your calculation, dependent on the magnitude and system. You can impose some sum-rules for the acoustic ones, to force them to be 0 at the Gamma point. Acoustic forces are harder to calculate (smaller forces). In your case I would guess up to 15 cm^1 should be ok for the acoustic ones. Negative optical ones should not occur. Best Marcel Mohr >> >> I was surfing this forum and FAQ and I found many discussion about >> negative frequencies, but I still cannot find the answers for me. >> >> Bac >> > > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > >
[Pw_forum] Strange phonon branches appear in phonon dispersion
your phonon branches are really strange... with two atoms I would expect 6 modes per each q-point stefano Viet Bac wrote: > Dear Pw_users, > > I am trying to do calculation phonon dispersion and EPC for 1D > Aluminum chain. I got the results which are strange phonon branches > appearing. In the case of 2 atom-cell, I got 4 phonon branches, two of > them are Optical and Acoustical phonon branches and two others, which > have zero and negative values, are unknown for me. In the case if I > have 1 atom-cell, that strange branch also appears. Could any body > explain for me what kind of frequencies here? > > I was surfing this forum and FAQ and I found many discussion about > negative frequencies, but I still cannot find the answers for me. > > Bac >
