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

[Md. Jahid Hasan Sagor]

 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: 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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> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
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