Thanks very much for your reply Saurabh, That's what I thought as well, though if the "omega" output by Espresso is a linear frequency it should be
Energy = h (energy-s) * nu (/s) 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. Best wishes, Johannes From: Saurabh Bajaj <sbajaj at caltech.edu<mailto:[email protected]>> Date: 21 September 2012 15:02:25 GMT+01:00 To: PWSCF Forum <pw_forum at pwscf.org<mailto:pw_forum at pwscf.org>> Subject: Re: [Pw_forum] Phonon omega or nu? Factors of 2pi Reply-To: PWSCF Forum <pw_forum at pwscf.org<mailto:pw_forum at pwscf.org>> Yes, you are right. The numbers with units /cm are wavenumbers (nu-bar). Frequency, nu (/s) = c (cm/s) * nu-bar (/cm) Lamda (cm) = 1/nu-bar (/cm) Energy = hbar (energy-s) * nu (/s) Saurabh Bajaj California Institute of Technology On Fri, Sep 21, 2012 at 9:25 AM, Johannes Moeller <j.moeller1 at physics.ox.ac.uk<mailto:j.moeller1 at physics.ox.ac.uk>> wrote: Hello all, 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? 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? 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. Many thanks, Johannes ------------------------------- Johannes Moeller Department of Physics University of Oxford Parks Road Oxford OX1 3PU, UK _______________________________________________ Pw_forum mailing list Pw_forum at pwscf.org<mailto:Pw_forum at pwscf.org> http://www.democritos.it/mailman/listinfo/pw_forum _______________________________________________ Pw_forum mailing list Pw_forum at pwscf.org<mailto:Pw_forum at pwscf.org> http://www.democritos.it/mailman/listinfo/pw_forum ------------------------------- Johannes Moeller Department of Physics University of Oxford Parks Road Oxford OX1 3PU, UK -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20120921/f782139f/attachment-0001.htm
