<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>Dear all,</div><div><br></div><div>Thanks for all your hints. Xhang, I had this feeling too and I did give a try to different version. At the end i managed to have no imaginary frequency. I am not 100% sure but it might be possible that sampling K-points with offset (i.e. 12 12 12 1 1 1) was giving troubles. Moreover i have increased up to 15 15 15 sampling with no offset. This is the kind of case where one belives to be converged (energy ok, structure ok etc) but you are not and phonon analysis tells you!</div><div><br></div><div>Now I stll have to fix a couple of issues becaus the soft modes Around gamma seems to be not perfectly linear wereas acustic should but this coud be a q-mash issue</div><div><br></div><div>I will keep u up to date</div><div><br></div><div>Vincenzo<br><br>Sent from my iPhone</div><div><br>On 25/ago/2014, at 16:25, Xiaolong Zhang <<a href="mailto:xlzhang.iop@gmail.com">xlzhang.iop@gmail.com</a>> wrote:<br><br></div><blockquote type="cite"><div><div dir="ltr"><div>Dear <span style="font-size:13px;font-family:arial,sans-serif;font-weight:bold;white-space:nowrap">Vincenzo Verdolino,</span></div><div><span style="font-size:13px;font-family:arial,sans-serif;font-weight:bold;white-space:nowrap"><br>
</span></div><div>Same problem here, and this could be version dependent. I tested a system with D3d symmetry. The QE4.3 and QE 5.1 give perfect phonon</div><div>dispersion, but with QE5.0.x there is always small imaginary frequencies around a high symmetric point (but not Gamma), you may try with</div>
<div>latest QE or with some older one (like 4.3). Hope this helps.</div><div><br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Aug 25, 2014 at 7:04 PM, Vincenzo Verdolino <span dir="ltr"><<a href="mailto:vincenzo.verdolino@gmail.com" target="_blank">vincenzo.verdolino@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto"><div>I have personally tested several things...PW cutoff, k sampling fft mash...everything...the only missing thing is the phonon tr2 value...i am doing that right now and let you know</div>
<div><br></div><div>Vincenzo<br><br>Sent from my iPhone</div><div><div class="h5"><div><br>On 25/ago/2014, at 12:51, "<a href="mailto:jzlhubei@gmail.com" target="_blank">jzlhubei@gmail.com</a>" <<a href="mailto:jzlhubei@gmail.com" target="_blank">jzlhubei@gmail.com</a>> wrote:<br>
<br></div><blockquote type="cite"><div>
<div><span></span>I have the similar problem with QE calculation with Phonon, I can not reproduece the result of an article for negative frequency around Gamma.</div><div>But I think that the tr2_ph to be <span style="font-family:宋体,Tahoma;font-size:14.399999618530273px;line-height:normal;background-color:window">1.0d-14 is enough.</span></div>
<div><span style="font-size:10.5pt;line-height:1.5;background-color:window">and recently I found Blog talks abount this question for negative frequency. BUt I can not get the idea why.I hope some senior user can give insight</span></div>
<div><span style="font-size:10.5pt;line-height:1.5;background-color:window">comment on this question</span></div><div><span style="font-size:10.5pt;line-height:1.5;background-color:window">the Blog web is </span><span style="background-color:window;font-size:10.5pt;line-height:1.5"><a href="http://blog.sina.com.cn/s/blog_5f15ead20101rhyj.html" target="_blank">http://blog.sina.com.cn/s/blog_5f15ead20101rhyj.html</a></span></div>
<div><br></div><hr style="width:210px;min-height:1px" color="#b5c4df" size="1" align="left">
<div><span><div style="MARGIN:10px;FONT-FAMILY:verdana;FONT-SIZE:10pt"><div><a href="mailto:jzlhubei@gmail.com" target="_blank">jzlhubei@gmail.com</a></div></div></span></div>
<blockquote style="margin-top:0px;margin-bottom:0px;margin-left:0.5em"><div> </div><div style="border:none;border-top:solid #b5c4df 1.0pt;padding:3.0pt 0cm 0cm 0cm"><div style="PADDING-RIGHT:8px;PADDING-LEFT:8px;FONT-SIZE:12px;FONT-FAMILY:tahoma;COLOR:#000000;BACKGROUND:#efefef;PADDING-BOTTOM:8px;PADDING-TOP:8px">
<div><b>From:</b> <a href="mailto:vincenzo.verdolino@gmail.com" target="_blank">Vincenzo Verdolino</a></div><div><b>Date:</b> 2014-08-25 17:05</div><div><b>To:</b> <a href="mailto:dalcorso@sissa.it" target="_blank">dalcorso</a>; <a href="mailto:pw_forum@pwscf.org" target="_blank">PWSCF Forum</a></div>
<div><b>Subject:</b> Re: [Pw_forum] Phonon calculation</div></div></div><div><div><div dir="ltr">Hi Andrea,<div><br></div><div><br></div><div>thank you for your answer, i will do that and give you updates if things get better.</div>
<div><br></div><div>Vincenzo </div></div><div class="gmail_extra"><br><br>
<div class="gmail_quote">On Mon, Aug 25, 2014 at 10:40 AM, Andrea Dal Corso <span dir="ltr"><<a href="mailto:dalcorso@sissa.it" target="_blank">dalcorso@sissa.it</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
I would start checking convergence with respect to tr2_ph.<br>
<br>
HTH,<br>
<br>
Andrea<br>
<br>
<br>
<br>
On Mon, 2014-08-25 at 07:25 +0200, Vincenzo Verdolino wrote:<br>
> _______________________________________________<br>
> Pw_forum mailing list<br>
> <a href="mailto:Pw_forum@pwscf.org" target="_blank">Pw_forum@pwscf.org</a><br>
> <a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a><br>
<span><font color="#888888"><br>
--<br>
Andrea Dal Corso Tel. 0039-040-3787428<br>
SISSA, Via Bonomea 265 Fax. 0039-040-3787249<br>
I-34136 Trieste (Italy) e-mail: <a href="mailto:dalcorso@sissa.it" target="_blank">dalcorso@sissa.it</a><br>
<br>
<br>
_______________________________________________<br>
Pw_forum mailing list<br>
<a href="mailto:Pw_forum@pwscf.org" target="_blank">Pw_forum@pwscf.org</a><br>
<a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a><br>
</font></span></blockquote></div><br></div>
</div></div></blockquote>
</div></blockquote><blockquote type="cite"><div><span>_______________________________________________</span><br><span>Pw_forum mailing list</span><br><span><a href="mailto:Pw_forum@pwscf.org" target="_blank">Pw_forum@pwscf.org</a></span><br>
<span><a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a></span></div></blockquote></div></div></div><br>_______________________________________________<br>
Pw_forum mailing list<br>
<a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
<a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a><br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div dir="ltr"><div>Xiao-Long Zhang<br></div>
<div><br><div>Ph.D student,<br><div>Institute of Physics, </div><div>Chinese Academy of Sciences</div><div>8 Nansanjie, Zhongguancun<br>Beijing 100190, China<br></div></div></div><div>Email: <a href="mailto:xlzhang@iphy.ac.cn" target="_blank">xlzhang@iphy.ac.cn</a> OR <a href="mailto:zgxolg@gmail.com" target="_blank">xlzhang.iop@gmail.com</a></div>
</div>
</div>
</div></blockquote><blockquote type="cite"><div><span>_______________________________________________</span><br><span>Pw_forum mailing list</span><br><span><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a></span><br><span><a href="http://pwscf.org/mailman/listinfo/pw_forum">http://pwscf.org/mailman/listinfo/pw_forum</a></span></div></blockquote></body></html>