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conway
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The Wikipedia article on the Helium Atom goes through the Thomas-Fermi approximation and shows that when you use a screening parameter Z you can optimize the energy of the atom according to the following formula:
\langle H \rangle = [-2Z^2 + \frac{27}{4}Z]E_1
(E_1 is elsewhere defined as the Rydberg unit -13.6 eV)
The minimum value for energy occurs for a choice of Z=1.69, and you can plug in the numbers (I did) to confirm that this gives a value of -77.45 eV for the helium atom.
QUESTION: The article then concludes by saying that using this value "we obtain the most accurate result yet:"
\frac{1}{2} \Bigg(\frac{3}{2}\Bigg)^6 = -77.5 eV
What is this formula? Of course it is a mistake because it is missing E_1; but that's not the problem. We can correct the mistake and just multiply 729/128 by 13.6 eV to get the quoted result. But how does this come from the original calculation? Where is the value Z=1.69 which came from the optimization?
\langle H \rangle = [-2Z^2 + \frac{27}{4}Z]E_1
(E_1 is elsewhere defined as the Rydberg unit -13.6 eV)
The minimum value for energy occurs for a choice of Z=1.69, and you can plug in the numbers (I did) to confirm that this gives a value of -77.45 eV for the helium atom.
QUESTION: The article then concludes by saying that using this value "we obtain the most accurate result yet:"
\frac{1}{2} \Bigg(\frac{3}{2}\Bigg)^6 = -77.5 eV
What is this formula? Of course it is a mistake because it is missing E_1; but that's not the problem. We can correct the mistake and just multiply 729/128 by 13.6 eV to get the quoted result. But how does this come from the original calculation? Where is the value Z=1.69 which came from the optimization?
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