Hello, Isn’t it possible to get IR spectra from the FFTs of the atomic velocity autocorrelation function?
Pascal Le 29 juil. 2015 à 17:58, Nicola Marzari <[email protected]> a écrit : > > Dear Yin, > > > you need to calculate at every time step the total dipole in the unit > cell, and then do the fourier transform of the autocorrelation - see e.g. > here: http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.81.1235 or many > other papers published on the topic. > > Note that if you do Car-Parrinello MD, rather than Born-Oppenhimer MD, > the vibrational frequencies can be slightly softened due to the fact > that the ions are dressed (and slowed down) by the coefficients of the > plane waves. The smaller the fictitious mass, the small the effect. > > Now, I'm not sure how to write the polarization at every time step - > maybe others can comment or add to the documentation. For PWSCF > you'd switch on lberry, but I'm not sure if you can do it during an > md (if now, maybe switch on lelfield, and then keep the applied field > equal to zero). > > In CP I suppose you could switch tefield on, but still have zero > applied field. > > Any other suggestion? Also, I think that tefield in CP and in PWSCF > mean different things - shall we switch the name in CP to lelfield? > > nicola > > > > On 29/07/2015 15:56, [email protected] wrote: >> Dear Quantum Espresso developers, >> >> I want to obtain IR spectra of crystals at room temperature. Considering >> the temperature effect, I decided to use CPMD. I wonder whether it is >> possible to get IR spectra from CPMD trajectory in Quantum Espresso? >> What's more, can I involve vdw-correction in CPMD? If yes, can IR >> spectra be calculated in the presence of vdw-correction? >> >> Thank you very much! >> >> Best Regards, >> ------------------------------------------------------------------------ >> Dr. Yin Li >> Department of Biophysics,Medical School, University of Pecs, >> No.12 Szigeti Street, Pecs, H-7624, HUNGARY >> Phone: +36-72-535271/36271 >> >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum >> > > -- > ---------------------------------------------------------------------- > Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL > Director, National Centre for Competence in Research NCCR MARVEL, EPFL > http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum -- Pascal Boulet - MCF HDR, Resp. L1 MPCI - DEPARTEMENT CHIMIE Aix-Marseille Université - ST JEROME - Avenue Escadrille Normandie Niemen - 13013 Marseille Tél: +33(0)4 13 55 18 10 - Fax : +33(0)4 13 55 18 50 Site : http://allos.up.univ-mrs.fr/pascal - Email : [email protected] Afin de respecter l'environnement, merci de n'imprimer cet email que si nécessaire.
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