<div dir="ltr">I will try changing the pseudopotential and repeat the calculations. I will report back to you as sson as my calculations are finish (will probably take a day to finish structure relaxation).</div><div class="gmail_extra">
<br><br><div class="gmail_quote">On Mon, Apr 14, 2014 at 2:12 AM, Sanjeev Gupta <span dir="ltr"><<a href="mailto:physics.skgupta@gmail.com" target="_blank">physics.skgupta@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="ltr">good. <div>can you take one more test to change the pseudo and see. May be I am wrong but see.</div><div><br></div><div><br><div><br></div><div> </div></div></div><div class="gmail_extra"><div><div class="h5">
<br><br><div class="gmail_quote">
On Sun, Apr 13, 2014 at 11:02 PM, ankit jain <span dir="ltr"><<a href="mailto:ankitjain.me.iitk@gmail.com" target="_blank">ankitjain.me.iitk@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="ltr">I have tried acoustic sum rule and it does not change negative frequencies. <div>I have rerun calculations with several different parameters and seems to have modified my vc-relax output file. I am re-running it and will send it as soon as it is done.</div>
</div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Apr 14, 2014 at 1:51 AM, Prasenjit Ghosh <span dir="ltr"><<a href="mailto:prasenjit.jnc@gmail.com" target="_blank">prasenjit.jnc@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="ltr"><div>Did you try using the acoustic sum rule and see whether the imaginary frequencies are still there? Also can I have a look at the vc-relax output file?<span><font color="#888888"><br>
<br></font></span></div><span><font color="#888888">Prasenjit<br></font></span></div><div><div><div class="gmail_extra">
<br><br><div class="gmail_quote">On 14 April 2014 11:10, ankit jain <span dir="ltr"><<a href="mailto:ankitjain.me.iitk@gmail.com" target="_blank">ankitjain.me.iitk@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="ltr">Hello Prasenjit,<div><br></div><div>I am getting negative phonon frequencies for non-gamma points also. After structure optimization, the total force is 0.000020 Ry/au and pressure is -0.24 kbar.</div><div>
<br>
</div><div>I am using ecutwfc of 100 Ry, which is converged with respect to the total energy of the system. I am not able to do convergence with respect to phonon modes as some modes have negative frequencies. Is there a way to do ecutwfc convergence for phonon modes without calculating phonon frequencies?</div>
<div><br></div><div>I am atatching my <a href="http://pw.in" target="_blank">pw.in</a>, <a href="http://ph.in" target="_blank">ph.in</a> pw.out and ph.out files (which I forgot to attch in my original mail) here.</div><div>
<br></div><div>Thanks,</div><div>
ANkit Jain </div></div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Apr 14, 2014 at 1:29 AM, Prasenjit Ghosh <span dir="ltr"><<a href="mailto:prasenjit.jnc@gmail.com" target="_blank">prasenjit.jnc@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="ltr"><div>For which q-point are you getting the imaginary modes? If it is at gamma, then it may be related to the instability in the structure, if it is at other q-points, may be lattice parameter is not properly optimized. How large is the stress you are getting at the end of the vc-relax calculation (when the code recalculates the total energy, stress and forces with the optimized lattice parameters & atomic positions). Also have you checked the convergence of the phonon modes with ecutwfc because typically the phonons converge much slowly with the size of the basis set than other parameters?<br>
<br></div><div>With regards,<br><br></div>Prasenjit<br></div><div class="gmail_extra"><br><br><div class="gmail_quote"><div><div>On 13 April 2014 21:55, Ankit <span dir="ltr"><<a href="mailto:ankitjain.me.iitk@gmail.com" target="_blank">ankitjain.me.iitk@gmail.com</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div>Hello QE developers and users,<br>
<br>
I am trying to calculate phonon dispersion using ph.x and matdyn.x<br>
routines of QE and I am stuck woth negative frequencies for a while now.<br>
<br>
I have a 1-D chain of polyethylene which has 6 atoms in the unit-cell.<br>
The polymer chain is aligned in z-direction and I have added vacuum on<br>
x- and y- direction. I did the structure relaxation and I am getting<br>
total force after relaxtion as 0.000020, which I guess is sufficiently<br>
small.<br>
<br>
After relaxation, when I am trying to calculate phonon dispersion using<br>
ph.x and matdyn.x I am getting netting frequencies for some of the<br>
phonon modes. I searched online and on QE mailing list and tried couple<br>
of different things:<br>
<br>
1. The negative frequencies are appearing for non-gamma point as well,<br>
so I guess its not a ASR issue. Anyway, I am using ASR but even after<br>
this I am getting negative frequencies.<br>
2. I reduced my tr2_ph and conv_thr to 1.0d-14 and 1.0d-15 which I guess<br>
are very small as suggested on QE FAQs.<br>
3. I checked phonon mode shapes for modes with negative frequencies and<br>
they do not look like rotational mode.<br>
4. I tried changing number of k points from 6 to 12 in z direction but<br>
this is also not the cause.<br>
<br>
I am really stuck here and not sure about the cause of negative<br>
frequencies. With vc-relax, my structure is getting relaxed which I<br>
guess means my structure is stable. But then I am not sure why I am<br>
getting negative frequencies.<br>
<br>
I really appreciate any help or suggestions.<br>
<br>
Thanks,<br>
<br>
Ankit Jain<br>
IIT Indore,<br>
Indore,<br>
India<br>
<br>
<br></div></div><div>
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</div></blockquote></div><span><font color="#888888"><br><br clear="all"><br>-- <br><div dir="ltr">PRASENJIT GHOSH,<br>IISER Pune,<br>Dr. Homi Bhabha Road, Pashan<br>Pune, Maharashtra 411008, India<br><br>
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Pune, Maharashtra 411008, India<br><br>Phone: <a href="tel:%2B91%20%2820%29%202590%208203" value="+912025908203" target="_blank">+91 (20) 2590 8203</a><br>Fax: <a href="tel:%2B91%20%2820%29%202589%209790" value="+912025899790" target="_blank">+91 (20) 2589 9790</a></div>
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<div><span style="font-size:13px;font-family:Tahoma"><br></span></div><div><span style="font-size:13px;font-family:Tahoma">------------------------------</span><span style="font-size:13px;font-family:Tahoma">------</span></div>
<div><div style="font-family:Tahoma;font-size:13px"><div style="font-size:13px"><div style="font-size:13px">Dr. Sanjeev Kumar Gupta<br>Fulbright Post-Doctoral Scholar<br>Dept. of Physics<br><span style="line-height:19.49652862548828px;text-align:justify;color:rgb(68,68,68);font-family:'Trebuchet MS',Geneva,sans-serif">Michigan Technological University </span><br>
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