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<p>Dear Professor Paulo and Fransesco,</p>
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<p>thanks for your help and suggestions</p>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" color="#000000" face="Calibri, sans-serif"><b>From:</b> pw_forum-bounces@pwscf.org <pw_forum-bounces@pwscf.org> on behalf of Paolo Giannozzi <p.giannozzi@gmail.com><br>
<b>Sent:</b> Thursday, August 25, 2016 12:41 PM<br>
<b>To:</b> PWSCF Forum<br>
<b>Subject:</b> Re: [Pw_forum] Negative freuqencies for extrapolating points</font>
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<div>I am aware of other cases in which acoustic phonon frequencies close to q=0 behave in a funny way. It happens in very small regions and resists to standard attempts (increasing convergence etc.) to get rid of it. No explanation and no fix available for
now.<br>
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Paolo<br>
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<div class="gmail_quote">On Thu, Aug 25, 2016 at 4:03 PM, Elio Physics <span dir="ltr">
<<a href="mailto:Elio-Physics@live.com" target="_blank">Elio-Physics@live.com</a>></span> wrote:<br>
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<div>Dear all,
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<p>I have calculated the frequencies for a structure. All frequencies were positive except for a few "extrapolated" points very close to the Gamma point which were negative in the range of -1.45 cm^-1. Due to this the dispersion curve near the Gamma point looked
a bit funny (but looks pretty good elsewhere). I tried the calculations with 2 different phonon grids. Any reason why this is happening? Do i have to lower tr2_ph more (it is already 10^(-19)!)</p>
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<p>Any help would be appreciated.</p>
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<p>Elio</p>
<p>Fed Uni of Rondonia</p>
Brazil</div>
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-- <br>
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<div>Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,<br>
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy<br>
Phone +39-0432-558216, fax +39-0432-558222<br>
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