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<div class="moz-cite-prefix">the phonon code calculate the second
order derivative of the energy at the given configuration.<br>
this can be done even the first order derivatives are non
vanishing.<br>
provided the structure is not too far from the minimum the
computed curvature can still quite close to the <br>
one one could have computed at equilibrium but it is an
approximation to it.<br>
<br>
stefano<br>
<br>
On 05/01/2013 05:18 PM, ding wrote:<br>
</div>
<blockquote cite="mid:tencent_2BD2545F335A8D770F04DD62@qq.com"
type="cite">
<pre wrap="">Dear everyone,
Does one have to relax the structure before doing phonon calculations? If I calculate the phonon dispersion of a material with the experimental structure at different pressures, Can I get get the phonon dispersions without negtive frequencies at different pressures ? I know that one has to optimize the structure before doing phonon calculation when using the small displacement method, but I am not sure if one has to optimize the structure before doing phonon calculations when using linear response theory. I want to calculate the electron-phonon interaction properties with the experimental structures at different pressures. If I don't optimize the structures, Can I get the phonon dispersions without negtive frequencies ?
Thanks in advance!</pre>
<br>
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