<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">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<div class=""><br class=""><div class="">
<span class="Apple-style-span" style="border-collapse: separate; font-variant-ligatures: normal; font-variant-position: normal; font-variant-numeric: normal; font-variant-alternates: normal; font-variant-east-asian: normal; line-height: normal; orphans: 2; text-indent: 0px; widows: 2; border-spacing: 0px;"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div class=""><span class="Apple-style-span" style="border-collapse: separate; font-variant-ligatures: normal; font-variant-position: normal; font-variant-numeric: normal; font-variant-alternates: normal; font-variant-east-asian: normal; line-height: normal; orphans: 2; text-indent: 0px; widows: 2; border-spacing: 0px;"><span class="Apple-style-span" style="border-collapse: separate; font-variant-ligatures: normal; font-variant-position: normal; font-variant-numeric: normal; font-variant-alternates: normal; font-variant-east-asian: normal; line-height: normal; orphans: 2; text-indent: 0px; widows: 2; border-spacing: 0px;"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><span style="font-size: 12px;" class="">— </span></div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div style="margin: 0px;" class=""><font class="Apple-style-span"><span style="font-size: 12px;" class="">Stefano Baroni - Trieste — </span><a href="http://stefano.baroni.me" style="color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-stroke-width: 0px;" class="">http://stefano.baroni.me</a><span style="font-size: 12px;" class=""> </span></font></div></div><div style="color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-stroke-width: 0px;" class=""><br class=""></div></div></div></div></div></div></div></span></span></div></div></div></span><br class="Apple-interchange-newline"><br class="Apple-interchange-newline">
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<div><br class=""><blockquote type="cite" class=""><div class="">On 9 Dec 2020, at 12:39, Tamas Karpati <<a href="mailto:tkarpati@gmail.com" class="">tkarpati@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">apart from the convergence issues negative frequencies from converged<br class="">calculations suggest<br class="">that your structure -as opposed to your standpoint- is not stable or<br class="">the geom. optimization was not<br class="">complete (many negative freqs. may indicate not being at the exact<br class="">energy minimum).<br class="">you can reoptimize (both cell and ions, ie. via vc-relax) the geometry<br class="">and next redo the phonon<br class="">sim. to check it.<br class=""><br class="">On Wed, Dec 9, 2020 at 11:47 AM Sohail Ahmad via users<br class=""><<a href="mailto:users@lists.quantum-espresso.org" class="">users@lists.quantum-espresso.org</a>> wrote:<br class=""><blockquote type="cite" class=""><br class="">Dear QE experts<br class="">I am trying to calculate the phonon of NiCrSi using QE 6.5.<br class=""><br class="">Either i get negative frequency or it does not converge<br class="">I tried with different values of convergence criteria, q mesh, alpha_mix in ph.in and k mesh in scf.in<br class=""><br class="">tr2_ph = 1.0d-14, or<br class="">tr2_ph = 1.0d-12, or<br class="">tr2_ph = 1.0d-16,<br class=""><br class="">nq1 = 4, nq2 = 4, nq3 = 4, or<br class="">nq1 = 3, nq2 =3, nq3 = 3, or<br class=""> nq1 = 2, nq2 = 2, nq3 =2,<br class=""><br class="">alpha_mix(1) = 0.7, or<br class=""> alpha_mix(1) = 0.3,<br class=""><br class="">K_POINTS<br class="">12 12 12 or<br class="">16 16 16<br class=""><br class="">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<br class="">Best Wishes<br class="">---------------------------------------------------------<br class=""><br class="">#phonon of NiCrSi structure<br class="">&inputph<br class="">prefix = 'NiCrSi',<br class="">tr2_ph = 1.0d-14,<br class="">ldisp = .true.,<br class="">nq1 = 4, nq2 = 4, nq3 = 4,<br class="">amass(1) = 51.99,<br class="">amass(2) = 28.08,<br class="">amass(3) = 58.69,<br class=""> alpha_mix(1) = 0.7,<br class="">outdir = './OUT',<br class="">fildyn = 'NiCrSi.dyn',<br class="">/<br class="">&control<br class=""> calculation = 'scf',<br class=""> restart_mode = 'from_scratch',<br class=""> prefix = 'NiCrSi',<br class=""> pseudo_dir = '/home/sohail/pseudo',<br class=""> outdir = './OUT',<br class="">/<br class="">&system<br class="">ibrav = 2, a = 5.4559000675, b = 5.4559000675, c = 5.4559000675,<br class="">cosAB = 0.0, cosBC = 0.0, cosAC = 0.0,<br class=""> nat = 3, ntyp = 3,<br class=""> ecutwfc = 75,<br class=""> ecutrho = 300,<br class=""> nbnd = 25,<br class=""> occupations = 'smearing', smearing = 'gaussian', degauss = 0.001,<br class="">/<br class="">&electrons<br class=""> mixing_beta = 0.3,<br class=""> conv_thr = 1.0d-9,<br class="">/<br class="">ATOMIC_SPECIES<br class="">Cr 51.99 Cr.pbe-sp-van.UPF<br class="">Si 28.08 Si.pbe-n-van.UPF<br class="">Ni 58.69 Ni.pbe-nd-rrkjus.UPF<br class="">ATOMIC_POSITIONS {alat}<br class="">Cr 0.00000000 0.00000000 0.00000000<br class="">Si 0.50000000 0.50000000 0.50000000<br class="">Ni 0.25000000 0.25000000 0.25000000<br class="">K_POINTS AUTOMATIC<br class="">12 12 12 0 0 0<br class=""><br class="">---------------------------------------------------------------------<br class=""><br class="">Sohail Ahmad<br class=""><br class="">Department of Physics<br class=""><br class="">Faculty of Science, P. O. Box - 9004<br class=""><br class="">King Khalid University<br class=""><br class="">Abha, Saudi Arabia<br class=""><br class="">--------------------------------------------------------------------<br class=""><br class="">_______________________________________________<br class="">Quantum ESPRESSO is supported by MaX (<a href="http://www.max-centre.eu" class="">www.max-centre.eu</a>)<br class="">users mailing list <a href="mailto:users@lists.quantum-espresso.org" class="">users@lists.quantum-espresso.org</a><br class=""><a href="https://lists.quantum-espresso.org/mailman/listinfo/users" class="">https://lists.quantum-espresso.org/mailman/listinfo/users</a><br class=""></blockquote>_______________________________________________<br class="">Quantum ESPRESSO is supported by MaX (<a href="http://www.max-centre.eu" class="">www.max-centre.eu</a>)<br class="">users mailing list <a href="mailto:users@lists.quantum-espresso.org" class="">users@lists.quantum-espresso.org</a><br class=""><a href="https://lists.quantum-espresso.org/mailman/listinfo/users" class="">https://lists.quantum-espresso.org/mailman/listinfo/users</a><br class=""></div></div></blockquote></div><br class=""></div></body></html>