[Pw_forum] Can I obtain IR spectrum from CPMD trajectory in Quantum Espresso?

[Pascal Boulet]

Thank you Paolo and Nicola for your answer.

Best
Pascal

Le 29 juil. 2015 à 18:16, Paolo Giannozzi <p.giannozzi at gmail.com> 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 <pascal.boulet at univ-amu.fr> 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 <nicola.marzari at epfl.ch> 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, liyincumt at gmail.com 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
>>> Pw_forum at pwscf.org
>>> 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
>> _______________________________________________
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> 
> --
> 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 : pascal.boulet at univ-amu.fr
> Afin de respecter l'environnement, merci de n'imprimer cet email que si nécessaire.
> 
> 
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> 
> 
> -- 
> Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
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--
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 : pascal.boulet at univ-amu.fr
Afin de respecter l'environnement, merci de n'imprimer cet email que si nécessaire.

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