I was thinking the other day, if you had the Schrodinger equation in 3-dimensions, and had a spherically symmetrical potential. Ie.: $$-\frac{ℏ^{2}}{2m}∇^{2}ψ+V(r)ψ=Eψ$$ Then you could simplify the Laplacian to: $$-\frac{ℏ^{2}}{2m}\frac{1}{r^{2}}\frac{∂}{∂r}\left(r^{2}\frac{∂ψ}{∂r}\right)+V(r)ψ(r)=Eψ(r)$$ The solution to this equation, doesn't correspond to the WKB solution, which if I recall correctly, is: $$\frac{A}{\sqrt{p\left(r\right)}}e^{\left(\frac{i}{ℏ}\int_{ }^{ }p\left(r\right)\ dr\right)}$$ Unless, you somehow remove the first-order term that turns up in the Laplacian - which I vaguely remember somewhere that you take the limit as $r$ approaches infinity. I don't know if this is what is suppose to be done, but if it is, then how is it viable? And if not, then could someone please explain how to solve this discrepancy. Edit: I want the states to also be spherically symmetrical. EDIT: I think I've found the solution, I made the substitution $$\frac{w\left(r\right)}{r}=ψ\left(r\right)$$ I then substituted this into the previous radial equation, and it gave me the regular TISE in 1 dimensions. This ultimately yields the WKB solution for ψ, which is : $$ψ\left(r\right)=\frac{1}{r}\frac{A}{\sqrt{p\left(r\right)}}e^{\left(\frac{i}{ℏ}\int_{ }^{ }p\left(r\right)\ dr\right)}$$
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5$\begingroup$ Does this answer your question? How to apply the WKB approximation in this case? $\endgroup$– G. SmithCommented Jun 5, 2021 at 7:05
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$\begingroup$ What happened to the angular terms in the Laplacian? $\endgroup$– G. SmithCommented Jun 5, 2021 at 7:07
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$\begingroup$ I assumed that the wave function only depended on radial distance. $\endgroup$– Matrix001Commented Jun 5, 2021 at 7:13
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$\begingroup$ All you said was “had a potential that was only dependent on the radial distance”. A spherically-symmetric potential has energy eigenstates that are asymmetric. I suggest editing your question to make clear you are interested only in the spherically-symmetric states. $\endgroup$– G. SmithCommented Jun 5, 2021 at 7:16
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I think I've found the solution, I made the substitution $$\frac{w\left(r\right)}{r}=ψ\left(r\right)$$ I then substituted this into the previous radial equation, and it gave me the regular TISE in 1 dimensions. This ultimately yields the WKB solution for ψ, which is : $$ψ\left(r\right)=\frac{1}{r}\frac{A}{\sqrt{p\left(r\right)}}e^{\left(\frac{i}{ℏ}\int_{ }^{ }p\left(r\right)\ dr\right)}$$