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In lecture, we discussed electron shielding as an additional influence in the interaction between electrons and ions. My understanding of shielding is that because of coulomb force, electrons have a higher probability of being near a nucleus (instead of being homogeneously distributed across space) and therefore shield the nuclei. In this way, regions of high (negative) charge density and regions of high atomic/positive charge density are created.
I understand this as a periodic effect, which I tried to illustrate in this sketch:

Distribution of electrons and Atoms

We also talked about the effect of overshielding, that there are too many electrons near the positive charge and that area is not just shielded and neutral, but overscreened and somewhat negatively charged. As far as I understand the effect, this also occurs with neutrally charged grids. So we also need areas that are positively charged on average. Wouldn't the electrons then have to go from the overscreened region to the positively charged region? This is clearly not the case as the Electric field is zero inside the conductor.

From this understanding, I either misunderstand overscreening as I don't see why we can have overshielding? Or I am missing a force that prevents this effect from immediately gets compensated?

Qmechanic
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mtooling
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1 Answers1

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In the static limit over screening is a quantum effect. Within classical electrostatics the minimum energy configuration is where the medium (electrons) work to suppress the interaction strength. In the quantum realm there are a few examples of overscreening. One of them is Friedel oscillations, a second example exploits the discreetness of charge and finally, to some extent the way Cooper pairs form in a superconductor is a result of "over screning."

Unfortunately, because it is a quantum effect by nature we lack physical intuition for it. You can not imagine a static distribution of charges and try to make sense out of that why the phenomena exists...

Jonathan Ruhman
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