I have to admit that an almost well relaxed structure may have no negative freqs. at all. I would like to add that the 6 lowest are still far from zero in this case which is an indicator, albeit not very clear (a few hundreds 1/cm can still be OK). Thanks for clarification.
On Wed, Dec 9, 2020 at 2:03 PM Stefano Baroni <bar...@sissa.it> wrote: > > I beg to differ. Whatever the specific reason may be in this case, negative > frequencies do *not* (necessarily) indicate incomplete relaxation, but the > fact that the nearest equilibrium structure is unstable (i.e. it is a saddle > point, rather than a minimum). If the current configuration is close enough > to a minimum, the computed frequencies should be positive no matter whether > you are at an equilibrium configuration or not. SB > > — > Stefano Baroni - Trieste — http://stefano.baroni.me > > > > > On 9 Dec 2020, at 12:39, Tamas Karpati <tkarp...@gmail.com> wrote: > > apart from the convergence issues negative frequencies from converged > calculations suggest > that your structure -as opposed to your standpoint- is not stable or > the geom. optimization was not > complete (many negative freqs. may indicate not being at the exact > energy minimum). > you can reoptimize (both cell and ions, ie. via vc-relax) the geometry > and next redo the phonon > sim. to check it. > > On Wed, Dec 9, 2020 at 11:47 AM Sohail Ahmad via users > <users@lists.quantum-espresso.org> wrote: > > > Dear QE experts > I am trying to calculate the phonon of NiCrSi using QE 6.5. > > Either i get negative frequency or it does not converge > I tried with different values of convergence criteria, q mesh, alpha_mix in > ph.in and k mesh in scf.in > > tr2_ph = 1.0d-14, or > tr2_ph = 1.0d-12, or > tr2_ph = 1.0d-16, > > nq1 = 4, nq2 = 4, nq3 = 4, or > nq1 = 3, nq2 =3, nq3 = 3, or > nq1 = 2, nq2 = 2, nq3 =2, > > alpha_mix(1) = 0.7, or > alpha_mix(1) = 0.3, > > K_POINTS > 12 12 12 or > 16 16 16 > > What could be the possible reason of getting negative frequency if the > structure is considered as stable ? Appreciate if someone point out the > possible mistakes > Best Wishes > --------------------------------------------------------- > > #phonon of NiCrSi structure > &inputph > prefix = 'NiCrSi', > tr2_ph = 1.0d-14, > ldisp = .true., > nq1 = 4, nq2 = 4, nq3 = 4, > amass(1) = 51.99, > amass(2) = 28.08, > amass(3) = 58.69, > alpha_mix(1) = 0.7, > outdir = './OUT', > fildyn = 'NiCrSi.dyn', > / > &control > calculation = 'scf', > restart_mode = 'from_scratch', > prefix = 'NiCrSi', > pseudo_dir = '/home/sohail/pseudo', > outdir = './OUT', > / > &system > ibrav = 2, a = 5.4559000675, b = 5.4559000675, c = 5.4559000675, > cosAB = 0.0, cosBC = 0.0, cosAC = 0.0, > nat = 3, ntyp = 3, > ecutwfc = 75, > ecutrho = 300, > nbnd = 25, > occupations = 'smearing', smearing = 'gaussian', degauss = 0.001, > / > &electrons > mixing_beta = 0.3, > conv_thr = 1.0d-9, > / > ATOMIC_SPECIES > Cr 51.99 Cr.pbe-sp-van.UPF > Si 28.08 Si.pbe-n-van.UPF > Ni 58.69 Ni.pbe-nd-rrkjus.UPF > ATOMIC_POSITIONS {alat} > Cr 0.00000000 0.00000000 0.00000000 > Si 0.50000000 0.50000000 0.50000000 > Ni 0.25000000 0.25000000 0.25000000 > K_POINTS AUTOMATIC > 12 12 12 0 0 0 > > --------------------------------------------------------------------- > > Sohail Ahmad > > Department of Physics > > Faculty of Science, P. O. Box - 9004 > > King Khalid University > > Abha, Saudi Arabia > > -------------------------------------------------------------------- > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list users@lists.quantum-espresso.org > https://lists.quantum-espresso.org/mailman/listinfo/users > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list users@lists.quantum-espresso.org > https://lists.quantum-espresso.org/mailman/listinfo/users > > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list users@lists.quantum-espresso.org > https://lists.quantum-espresso.org/mailman/listinfo/users _______________________________________________ Quantum ESPRESSO is supported by MaX (www.max-centre.eu) users mailing list users@lists.quantum-espresso.org https://lists.quantum-espresso.org/mailman/listinfo/users