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

[Alex Kirkpatrick]

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'?

Kind regards,


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________________________________
From: Lorenzo Paulatto <lorenzo.paulatto at cnrs.fr>
Sent: 29 August 2024 11:27
To: Alex Kirkpatrick <canilivehere at hotmail.co.uk>; Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
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 <users-bounces at lists.quantum-espresso.org><mailto:users-bounces at lists.quantum-espresso.org> on behalf of Lorenzo Paulatto <lorenzo.paulatto at cnrs.fr><mailto:lorenzo.paulatto at cnrs.fr>
Sent: 29 August 2024 10:15
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org><mailto: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><mailto: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


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Dr. Lorenzo Paulatto
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