Coulomb WKB quantization with the Langer correction (source code)

= Coulomb WKB quantization with the Langer correction
{c}

After the logarithmic radial coordinate $r=e^x$, the Langer replacement $l(l+1)\mapsto(l+1/2)^2$ turns the radial Coulomb problem into a two-turning-point <WKB approximation> problem. Its action integral gives
$$
E_{n,l}\sim-\frac{mV_0^2}{2\hbar^2(n+l+1)^2},
$$
which in this Coulomb case agrees with the exact dependence on the principal quantum number.