[QE-users] Pseudopotential to approximate a free electron?

[Lorenzo Paulatto]

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
>
> Sent from Outlook <http://aka.ms/weboutlook>
>
>
> ------------------------------------------------------------------------
> *From:* users <users-bounces at lists.quantum-espresso.org> on behalf of 
> Lorenzo Paulatto <lorenzo.paulatto at cnrs.fr>
> *Sent:* 29 August 2024 10:15
> *To:* Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
> *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 
> <canilivehere at hotmail.co.uk> 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/ - https://anharmonic.github.io/
23-24/423 B115, 4 place Jussieu 75252 Paris CX 05
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