When applying WKB approximation method to the radial Schrödinger equation, − − ℏ ℏ 2 2 m d 2 R ( r ) d r 2 + [ E − − V eff ( r ) ] R ( r ) = 0 , where the effective potential is given by V eff ( r ) = V ( r ) − − ℏ ℏ 2 ℓ ℓ ( ℓ ℓ + 1 ) 2 m r 2 ( ℓ ℓ the azimuthal quantum number related to the angular momentum operator), the eigenenergies and the wave function behaviour obtained are different from the real solution.