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<div>Thanks very much for your reply Saurabh, </div>
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<div>That's what I thought as well, though if the "omega" output by Espresso is a linear frequency it should be </div>
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<div>Energy = h (energy-s) * nu (/s)</div>
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<div>rather than hbar. This is not what I would naturally do if I was a given a number "omega". So if this indeed is correct, I think the naming of the phonon output frequency should be revised. </div>
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<div>Best wishes,</div>
<div>Johannes</div>
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<span style="font-family:'Helvetica'; font-size:medium; color:rgba(127, 127, 127, 1.0);"><b>From:
</b></span><span style="font-family:'Helvetica'; font-size:medium;">Saurabh Bajaj <<a href="mailto:sbajaj@caltech.edu">sbajaj@caltech.edu</a>><br>
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<span style="font-family:'Helvetica'; font-size:medium; color:rgba(127, 127, 127, 1.0);"><b>Date:
</b></span><span style="font-family:'Helvetica'; font-size:medium;">21 September 2012 15:02:25 GMT+01:00<br>
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<span style="font-family:'Helvetica'; font-size:medium; color:rgba(127, 127, 127, 1.0);"><b>To:
</b></span><span style="font-family:'Helvetica'; font-size:medium;">PWSCF Forum <<a href="mailto:pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br>
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<span style="font-family:'Helvetica'; font-size:medium; color:rgba(127, 127, 127, 1.0);"><b>Subject:
</b></span><span style="font-family:'Helvetica'; font-size:medium;"><b>Re: [Pw_forum] Phonon omega or nu? Factors of 2pi</b><br>
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<div>Yes, you are right. The numbers with units /cm are wavenumbers (nu-bar). </div>
<div>Frequency, nu (/s) = c (cm/s) * nu-bar (/cm)</div>
<div>Lamda (cm) = 1/nu-bar (/cm)</div>
<div>Energy = hbar (energy-s) * nu (/s)</div>
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<div> </div>
<div>Saurabh Bajaj</div>
<div>California Institute of Technology<br>
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<div class="gmail_quote">On Fri, Sep 21, 2012 at 9:25 AM, Johannes Moeller <span dir="ltr">
<<a href="mailto:j.moeller1@physics.ox.ac.uk" target="_blank">j.moeller1@physics.ox.ac.uk</a>></span> wrote:<br>
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<div>Hello all, </div>
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<div>A quick question about the definition of the phonon frequency omega. Is the omega output by Espresso an angular or a linear frequency (omega/2pi)? I.e. is this converted into an energy by multiplying by hbar or h? </div>
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<div>Comparing simple vibrational modes of molecules (eg. of CO2) in cm^-1 to experimental values gives good agreement with experimental data, which are usually referred to as a liner frequency nu or 1/lambda rather than an angular frequency omega. This suggests
that the value that Espresso outputs is nu and not omega(2pi*nu) as the name implies? </div>
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<div>The values output by Espresso in THz and cm^-1 seem to be related simply by a factor of c (no factors of 2pi). I'm using QE 5.01 but I don't think this is version specific. </div>
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<div>Many thanks,</div>
<div>Johannes</div>
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