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

[Pascal Boulet]

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
>> 
>> 
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>> 
> 
> -- 
> ----------------------------------------------------------------------
> 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
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