Thank you Paolo and Nicola for your answer. Best Pascal
Le 29 juil. 2015 à 18:16, Paolo Giannozzi <[email protected]> a écrit : > From the FFTs of the atomic velocity autocorrelation function you can extract > phonon frequencies, but you do not get "true" spectra > > Paolo > > On Wed, Jul 29, 2015 at 6:08 PM, Pascal Boulet <[email protected]> > wrote: > 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. > > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum > > > > -- > Paolo Giannozzi, Dept. Chemistry&Physics&Environment, > Univ. Udine, via delle Scienze 208, 33100 Udine, Italy > Phone +39-0432-558216, fax +39-0432-558222 > _______________________________________________ > 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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