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<p>In my experience, increasing also the convergence for forces and
total energy of the scf cycle you perform before the neb.x run,
helps a lot to clean negative frequencies.</p>
<p><br>
</p>
<p>Then, all other cutoffs and settings that increase amount of
memory and cpu time, can helps, sometimes significantly, sometimes
their not enough.</p>
<p><br>
</p>
<p>Before the phonon, a proper lattice relaxation with higher
parameters than default value for forces, total energy and
eventually even electron convergence (as also wavefunction, charge
density, etc..), helps much more to bring your model to the
highest converged condition than just increasing parameters
thresholds on phonon that can make the phonon a jurassic waiting.</p>
<p><br>
</p>
<p>These are the reflections helped me more</p>
<p><br>
</p>
<p>Francesco</p>
<p>Strathclyde</p>
<p><br>
</p>
<p><br>
</p>
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<div class="moz-cite-prefix">On 25/08/16 15:03, Elio Physics wrote:<br>
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<div>Dear all,
<p><br>
</p>
<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>
<p><br>
</p>
<p>Any help would be appreciated.</p>
<p><br>
</p>
<p>Elio</p>
<p>Fed Uni of Rondonia</p>
Brazil</div>
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