Meaning of the potential

[HexagonReversal]

Hi all,

I have been thinking about the meaning of the potential curve in the Al surface energy calculation exercise. The vacuum potential is easy to understand, but what about the energy in the middle of the slab? That value is about -0.275 Ry = -3.73 eV. Does it has any meaning? Does the energy difference between the vacuum potential and this value has any meaning?

The Fermi energy is 1.826 eV. It is about the energy of the highest occupied level. Since we are using pseudopotentials, we are only considering the valance electrons, which should have the energy around this level. But then why does the potential in the middle of slab so low?

I am also wondering if the Fermi energy calculation using a slab is appropriate. The Fermi energy of a bulk crystal should be different from the one that is 3-atom-layer-thin, right? Will that render our calculated surface energy useless?

Thanks in advance!

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Also want to draw some attention to my post in the previous chapter https://compmatphys.org/forums/topic/the-correct-tio2-contunnite-structure/

[HexagonReversal]

Correction: it is not the “surface energy” exercise, but the “work function” calculation exercise. This one: https://compmatphys.org/wp-content/uploads/2022/09/work-function.pdf

[HexagonReversal]

One last question: is the Fermi energy, like the total energy, depends strongly on the choice of pseudo-potential and reference energy, such that it cannot be directly compared when a different pseudo-potential is used?

[HexagonReversal]

>I am also wondering if the Fermi energy calculation using a slab is appropriate. The Fermi energy of a bulk crystal should be different from the one that is 3-atom-layer-thin, right? Will that render our calculated surface energy useless?

I figured out this question myself now. The work function is a surface property, not a bulk property. So that justifies the use of a slab for the Fermi energy calculation. But according to Wikipedia:

“The work function refers to removal of an electron to a position that is far enough from the surface (many nm) that the force between the electron and its image charge in the surface can be neglected.”

This will certainly introduce some error with our very thin slab, right? Wouldn’t it better if we calculate the Fermi energy with a full crystal instead?

• This reply was modified 2 years ago by HexagonReversal.

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