<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman,new york,times,serif;font-size:12pt">Dear Hao,<br><br><pre>> The kpoint grid I chose is 60*60*60. <br> <br>I suppose you vast time with such kind incredibly large k-mesh.<br><br>Try increasing nq's for phonon calculations (ph.in). Play around <br>cutoff energy and the threshold parameter for phonons.<br><br>What is the accuracy of your q2r.x (FFT) run?<br><br>Bests,<br>Eyvaz.<br></pre>-------------------------------------------------------------------<br>Prof. Eyvaz Isaev, <br>Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden <br>Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, <br>isaev@ifm.liu.se, eyvaz_isaev@yahoo.com<div><br></div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><br><div style="font-family: times new
roman,new york,times,serif; font-size: 12pt;"><font face="Tahoma" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> HaoPan <adehaopan@hotmail.com><br><b><span style="font-weight: bold;">To:</span></b> pw_forum@pwscf.org<br><b><span style="font-weight: bold;">Sent:</span></b> Thu, July 29, 2010 9:49:32 PM<br><b><span style="font-weight: bold;">Subject:</span></b> [Pw_forum] Fourier interpolation<br></font><br>
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<pre>Dear Baroni,<br><br>The kpoint grid I chose is 60*60*60. <br> nk1=60, nk2=60, nk3=60,<br><br>I think that is fine enough. Because the q point grid is just 6*6*6. <br>For metal, the frequencies of the gamma point are alway not zero (some small negative value) . <br>Some may cause the frequencies around the gamma point negative. But even all q points I got are <br>positive, there exit negative frequencies after the matdyn.x calculation. I don't know why.<br><br>Sincerely,<br>Pan Hao<br>Tulane University<br><br><br>the kpoint grid you are using may be too coarse<br>dynamical matrices in metals are indeed smooth functions of k, unless you have Kohn anomalies<br>SB<br><br>On Jul 28, 2010, at 5:33 PM, HaoPan wrote:<br><br>><i> Hi, everyone,<br></i>><i> <br></i>><i> On each q point I got, the phone frequencies are positive. But after the Fourier interpolation process, There<br></i>><i> exist negative frequencies. I check the some
special q points using ph.x, there are no negative frequencies. I<br></i>><i> know the dynamical matrices for metal are not smooth function of q, but how do I fix it to get the right<br></i>><i> dispersion curves? Thanks a lot.<br></i>><i> <br></i>><i> Sincerely,<br></i>><i> Pan Hao<br></i>><i> Tulane University _______________________________________________<br></i>><i> Pw_forum mailing list<br></i>><i> <a rel="nofollow" target="_blank" href="http://www.democritos.it/mailman/listinfo/pw_forum">Pw_forum at pwscf.org</a><br></i>><i><span> <a target="_blank" href="http://www.democritos.it/mailman/listinfo/pw_forum">http://www.democritos.it/mailman/listinfo/pw_forum</a></span><br></i></pre> </div></div>
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