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

[Lorenzo Paulatto]

Hello Jahid,

I have read the article very quickly, but I do not think they use the 
RMS to compute epsilon. All they do is compute epsilon for a few sample 
atomic potisions reached during the MD run, then they average it. The 
"Theoretical Method" section does not have any logic, but it is 
explained in the "Conclusions". The RMS seems to be only used to 
ascertain the validity of the simulation.

hth

On 1/11/24 04:42, Md. Jahid Hasan Sagor wrote:
> Hi Dr. Paulatto,
>
> Thank you so much for your comments.
>
> Actually, The paper (attached) 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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