Dear Bipul,<div><br></div><div>I haven't done such kind of calculation. However, when reading your question, there are couple of questions that may help you:</div><div><br></div><div>1. Did you perform the STRUCTURE convergence test for K-point mesh and/or energy cutoff?</div>
<div>2. Did you use the relaxed equilibrium structure which was obtained by using 10x10x10 mesh and 32Ry cutoff to perform 14x14x14 mesh and 38Ry cutoff phonon calculation?</div><div>3. How about the forces acting on the atoms in 2 cases? Are they too different?</div>
<div><br></div><div>Hope those help!</div><div><br></div><div>-------------------------------------------------</div><div>Duy Le</div><div>PhD Student.</div><div>University of Central Florida.<br><br><div class="gmail_quote">
On Sun, Aug 23, 2009 at 12:46 PM, Bipul Rakshit <span dir="ltr"><<a href="mailto:bipulrr@gmail.com">bipulrr@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Dear Pwscf users,<br>
I have a question about phonon calculation.<br>
I am doing phonon of K2S (antifluorite structure), using 10x10x10<br>
k-points mesh. In that calculations i find -ve frequencies.<br>
<br>
But then on increasing the mesh 14x14x14 and also the kinetic energy<br>
cutoff from 32 to 38 Ry, now i am getting all the +ve freq.<br>
<br>
Can you please tell me the reason or give me some reference, so that<br>
by reading that i can understand the things.<br>
<br>
regards<br>
--<br>
Bipul Rakshit<br>
Research Fellow,<br>
S N Bose Centre for Basic Sciences,<br>
Salt Lake,<br>
Kolkata 700 098<br>
India<br>
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</blockquote></div><br><br clear="all"><br>-- <br>Men don't need hands to do things!<br>
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