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

Fri Jul 31 09:59:22 CEST 2015

Thank you Giuseppe for your answer.

Best,
Pascal

Le 29 juil. 2015 à 23:26, Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it> a écrit :

> 
> 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
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> 
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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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