[QE-users] Requested some guidelines in First-principles molecular dynamics

[Lorenzo Paulatto]

p.s. Have a look at 
https://journals.aps.org/prb/pdf/10.1103/PhysRevB.94.075125 where the 
temperature dependent spectrum is in fact computed from the RMS

hth

On 1/11/24 04:46, Md. Jahid Hasan Sagor wrote:
> Hi Dr. Paulatto,
>
> Thank you so much for your comments.
>
> Actually, The paper ( https://doi.org/10.1103/PhysRevB.77.125218 ) 
> extracted the temperature of each configuration from the mean square 
> displacement per atom of the configuration (GaAs). In the harmonic 
> approximation, they determined the relationship between mean square 
> displacement and temperature T from the phonon density of states of 
> bulk GaAs calculated by Giannozzi et al. The equation as follows:
>
> image.png
> Here is the figure they generated
> image.png
>
>
> So, now If I can find out the RMS of GaAs using CPMD, I will try to 
> observe the corresponding configuration of GaAs atoms. Finally, the 
> atomic positions will be the input of Quantum Espresso pw.x etc ( I 
> mean normally how do we calculate dielectric constant in QE).
>
> Can I use  it ( https://anharmonic.github.io/thermal2/#d3_r2qx-code) 
> for the same purpose?
>
> Best
> Hasan
>
> On Wed, Jan 10, 2024 at 3:13 PM Lorenzo Paulatto 
> <lorenzo.paulatto at cnrs.fr> wrote:
>
>     I would guess that you calculate the static dielectric constant at
>     the temperature-dependent volume (experimental, or quasi-harmonic)
>     and you are 90% of the way there. Do you have a specific reason to
>     believe that it would be proportional to the RMS ?
>
>     Btw, the code d3_r2q.x included with the "anharmonic" package can
>     compute the RMS from an inexpensive phonon calculation, maybe have
>     a look at it before doing a large supercell MD.
>
>     https://anharmonic.github.io/thermal2/#d3_r2qx-code
>
>     cheers
>
>     On 10/01/2024 19:35, Md. Jahid Hasan Sagor wrote:
>>     Actually, I have to calculate Dielectric constant for GaAs for
>>     different temperatures (not 0 k). To do that, I need to extract
>>     atomic positions for different RMS using CPMD. If anyone know
>>     someone/ or give some guidelines, it would be great help for me.
>>
>>     Thank you.
>>
>>     On Tue, Jan 9, 2024, 2:09 PM Md. Jahid Hasan Sagor
>>     <md.sagor at maine.edu> wrote:
>>
>>         Dear QE community,
>>
>>         I want to calculate the mean square displacement of GaAs
>>         using CPMD. From the mean square displacement, I want to
>>         extract the configuration of atoms (e.g atomic position of Ga
>>         and As). Could anyone please give me some guidelines on how I
>>         can perform it? Should I use only the cp.x package or by
>>         other means? Your time and suggestions would be a great help
>>         for me.
>>
>>         Best Regards
>>         Md Jahid Hasan
>>         PhD Student, Mechanical Engineering
>>         University of Maine
>>
>>
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>     -- 
>     Dr. Lorenzo Paulatto
>     IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
>     phone: +33 (0)1 442 79822 / skype: paulatz
>     http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
>     23-24/423 B115, 4 place Jussieu 75252 Paris CX 05
>     _______________________________________________
>     The Quantum ESPRESSO community stands by the Ukrainian
>     people and expresses its concerns about the devastating
>     effects that the Russian military offensive has on their
>     country and on the free and peaceful scientific, cultural,
>     and economic cooperation amongst peoples
>     _______________________________________________
>     Quantum ESPRESSO is supported by MaX (www.max-centre.eu
>     <http://www.max-centre.eu>)
>     users mailing list users at lists.quantum-espresso.org
>     https://lists.quantum-espresso.org/mailman/listinfo/users
>
-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
23-24/423 B115, 4 place Jussieu 75252 Paris CX 05
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