<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Hello,<div><br></div><div>Isn’t it possible to get IR spectra from the FFTs of the atomic velocity autocorrelation function?</div><div><br></div><div>Pascal</div><div><br><div><div>Le 29 juil. 2015 à 17:58, Nicola Marzari <<a href="mailto:nicola.marzari@epfl.ch">nicola.marzari@epfl.ch</a>> a écrit :</div><br class="Apple-interchange-newline"><blockquote type="cite"><br>Dear Yin,<br><br><br>you need to calculate at every time step the total dipole in the unit<br>cell, and then do the fourier transform of the autocorrelation - see e.g.<br>here: <a href="http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.81.1235">http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.81.1235</a> or many<br>other papers published on the topic.<br><br>Note that if you do Car-Parrinello MD, rather than Born-Oppenhimer MD,<br>the vibrational frequencies can be slightly softened due to the fact<br>that the ions are dressed (and slowed down) by the coefficients of the<br>plane waves. The smaller the fictitious mass, the small the effect.<br><br>Now, I'm not sure how to write the polarization at every time step -<br>maybe others can comment or add to the documentation. For PWSCF<br>you'd switch on lberry, but I'm not sure if you can do it during an<br>md (if now, maybe switch on lelfield, and then keep the applied field<br>equal to zero).<br><br>In CP I suppose you could switch tefield on, but still have zero<br>applied field.<br><br>Any other suggestion? Also, I think that tefield in CP and in PWSCF<br>mean different things - shall we switch the name in CP to lelfield?<br><br><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>nicola<br><br><br><br>On 29/07/2015 15:56, <a href="mailto:liyincumt@gmail.com">liyincumt@gmail.com</a> wrote:<br><blockquote type="cite">Dear Quantum Espresso developers,<br><br>I want to obtain IR spectra of crystals at room temperature. Considering<br>the temperature effect, I decided to use CPMD. I wonder whether it is<br>possible to get IR spectra from CPMD trajectory in Quantum Espresso?<br>What's more, can I involve vdw-correction in CPMD? If yes, can IR<br>spectra be calculated in the presence of vdw-correction?<br><br>Thank you very much!<br><br>Best Regards,<br>------------------------------------------------------------------------<br>Dr. Yin Li<br>Department of Biophysics,Medical School, University of Pecs,<br>No.12 Szigeti Street, Pecs, H-7624, HUNGARY<br>Phone: +36-72-535271/36271<br><br><br>_______________________________________________<br>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>http://pwscf.org/mailman/listinfo/pw_forum<br><br></blockquote><br>-- <br>----------------------------------------------------------------------<br>Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL<br>Director, National Centre for Competence in Research NCCR MARVEL, EPFL<br><a href="http://theossrv1.epfl.ch/Main/Contact">http://theossrv1.epfl.ch/Main/Contact</a> <a href="http://nccr-marvel.ch/en/project">http://nccr-marvel.ch/en/project</a><br>_______________________________________________<br>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>http://pwscf.org/mailman/listinfo/pw_forum<br></blockquote></div><br><div>
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