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

[Md. Jahid Hasan Sagor]

Hi Dr. Paulatto,

Thank you so much for your suggestions. I was going in the wrong direction.
So if I use your recommended code (
https://anharmonic.github.io/thermal2/#d3_r2qx-code), would I be able to
generate the following figure for Bulk GaAs?

[image: image.png]

Actually my main goal is to calculate dielectric function at different
temperatures (not 0 K).

Thanks
Md Jahid Hasan

On Thu, Jan 11, 2024 at 9:19 AM Lorenzo Paulatto <lorenzo.paulatto at cnrs.fr>
wrote:

> 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: image.png]
> Here is the figure they generated
> [image: 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)
>> 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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