On 1/11/24 20:57, Md. Jahid Hasan Sagor wrote:
Hi Dr. Paulatto,
Thank you for your advice. I also like your idea about epsilon.x. But
the dielectric function we get using epsilon.x (QE), Isn't it for only
0 K? How can I extend it to another temperature?
It is computed with an electronic temperature of 0K, but it is exactly
the same as in the paper you are trying to reproduce. But this is not a
big deal, there is very little direct effect of temperature on
electrons: compare the energy of thermal excitation (k_B T) with the
band gap of GaAs and you will see why. I.e. electron orbitals are far
too rigid to be affected by temperature, especially in insulators. Even
in metal we use fictitious electronic temperature to speed up
integration (aka smearing) that is of the order of 1'000K, and it does
not change the electronic structure much. The effect only come through
the motion of ions, so move the ions and you got finite temperature.
But do not believe me: change the electronic occupation to "smearing"
and set a Fermi-Dirca smearing which is equivalent to the temperature
you want (it is in Ry, i.e. 1 Ry = 157'887 K). Then see how, much the
total energy and band structure change. how many k-points do you need to
have a discernible Fermi surface at the to of valence band, etc.
hth
Best
Md Jahid
On Thu, Jan 11, 2024 at 2:36 PM Lorenzo Paulatto
<lorenzo.paula...@cnrs.fr> wrote:
On 11/01/2024 20:06, Md. Jahid Hasan Sagor wrote:
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?
No. The anharmonic code is about vibrational properties.
Actually my main goal is to calculate dielectric function at
different temperatures (not 0 K).
You can try to do like in the paper. Or you can try a different
approach, i.e. replacing the sampling via molecular dynamics with
a stochastic sampling, like the one provided by the SSCHA code
http://sscha.eu/, which is also compatible with QE. Anyway, the
supercell they use is tiny (8 atoms, which is just the
simple-cubic form of GaAs), you should be able to use the
epsilon.x code that comes with QE (check the manual in
PP/Doc/man_eps.pdf). I would say, start with just epsilon as a
function of the volume, test convergence and see if you can afford
it,.
kind regards
Thanks
Md Jahid Hasan
On Thu, Jan 11, 2024 at 9:19 AM Lorenzo Paulatto
<lorenzo.paula...@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.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.paula...@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.sa...@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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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>)
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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
--
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
--
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@lists.quantum-espresso.org
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