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

[Giuseppe Mattioli]

Dear Pascal
If I remember well, you can obtain the cell dipole trajectory by  
adding assume_isolated='mp' to your cp.x molecular dynamics input of a  
system contained in a cubic cell (mp is defined for cubic cells only).  
But the system should be really "isolated" (e.g., a molecule with its  
center of mass always near to the center of the box) or you may have  
jumps in the dipole due to PBC which should result in noise when you  
FFT the dipole autocorrelation function. In my experience (an isolated  
Co-oxo cluster), it was the only way to obtain an IR spectrum in a  
DFT+U framework (DFPT still does not work together with DFT+U). It  
should be also useful in the case of vdw corrections implemented in  
cp.x.
HTH
Giuseppe

Quoting Pascal Boulet <pascal.boulet at univ-amu.fr>:

> 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
>>> _______________________________________________
>>> Pw_forum mailing list
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>>> 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 :  
>> 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
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> 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 : pascal.boulet at univ-amu.fr
> Afin de respecter l'environnement, merci de n'imprimer cet email que  
> si nécessaire.


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    Giuseppe Mattioli
    CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
    v. Salaria Km 29,300 - C.P. 10
    I 00015 - Monterotondo Stazione (RM)
    Tel + 39 06 90672836 - Fax +39 06 90672316
    E-mail: <giuseppe.mattioli at ism.cnr.it>