On 29/08/2024 14:25, Alex Kirkpatrick wrote:
You've given me an interesting direction to follow, thanks for the info!
Just for curiosity's sake, is the problem with the idea of 'adding a
free electron pseudo' because it means a very different thing in QE
code than 'adding a particle to the simulation that acts like an
electron'?
A pseudopotential is a modelisation of the atom nuclei + the core
electrons which are assumed to be rigid, and their effect on the valence
atoms. It is inherently a rigid object. You choose where to put the
pseudopotentials in the unit cell, then the code adds the necessary
amount of electrons to neutralize them, these electrons are free to
delocalize and float around in order to minimize the total energy.
It is not totally completely absurd to conceive a pseudopotential like a
point-charge has a negative charge, i.e. a potential of form -q/r, then
assign to it the electron mass and compute the force acting on it, but
it would probably break a lot of implicit assumptions that have been
made in the code.
For example, I once tried to do a pseudopotential for a noble gas with
zero electrons in valence, and it totally did not work properly, what
you propose is even more extreme.
hth
Kind regards,
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------------------------------------------------------------------------
*From:* Lorenzo Paulatto <[email protected]>
*Sent:* 29 August 2024 11:27
*To:* Alex Kirkpatrick <[email protected]>; Quantum ESPRESSO
users Forum <[email protected]>
*Subject:* Re: [QE-users] Pseudopotential to approximate a free electron?
On 29/08/2024 12:36, Alex Kirkpatrick wrote:
Thanks for the reply Lorenzo.
I'm very new to all this but my thought was that, to have some
control over the distance between the 'electron' and the surface,
I would need to include it as a discrete entity.
Hello, QE is a code based on plane waves, which means that you cannot
choose where an electron goes. But I don't think you need to use an
explicit electron for your task. Thank to the power of numerical
simulation, you can plot/measure directly the magnitude of the
Kohn-Sham potential, (which is identical to the Hartree electrostatic
potential when you go in the vacuum).
The procedure is similar to the one explained in the workfunction
example (PP/examples/WorkFct_example) which shows how to compute the
average value of the electrostatic potential far away in the vacuum to
estimate the energy required to pull an electron from the surface out
to infinity.
Of course the procedure is not entirely self-consistent (i.e. pulling
out the electron would change the potential) but for a metal it is
very close, and if you really need to you can remove some amount of
charge fro mthe surface using a positive value for tot_charge
hth
I would then be able to vary the distance and see how things
change. Is this the wrong way to go about it?
Kind regards
Alex
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------------------------------------------------------------------------
*From:* users <[email protected]>
<mailto:[email protected]> on behalf of
Lorenzo Paulatto <[email protected]>
<mailto:[email protected]>
*Sent:* 29 August 2024 10:15
*To:* Quantum ESPRESSO users Forum
<[email protected]>
<mailto:[email protected]>
*Subject:* Re: [QE-users] Pseudopotential to approximate a free
electron?
You could, probably, but why not just use tot_charge=-1
Kind regards
On August 29, 2024 10:03:30 AM GMT+02:00, Alex Kirkpatrick
<[email protected]>
<mailto:[email protected]> wrote:
Dear all,
Is it possible to create a pseudopotential file, or modify an
existing one like hydrogen, to approximate placing a free
electron in the simulation cell?
The end goal being to model its interaction with material
surfaces in vacuum.
Best wishes,
Alex
Sent from Outlook <http://aka.ms/weboutlook>
--
Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/
<http://www.impmc.upmc.fr/~paulatto/> - https://anharmonic.github.io/
<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
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