The path integral formulation can reproduce the right energy spectrum of the harmonic oscillator potential, but it cannot resolve the Coulomb potential problem. This is because the path integral cannot properly take into account the boundary condition, which is due to the presence of the scattering states in the Coulomb potential system. On the other hand, the Sommerfeld quantization can reproduce the right energy spectrum of both harmonic oscillator and Coulomb potential cases since the boundary condition is effectively taken into account in this semiclassical treatment. The basic difference between the two schemes should be that no constraint is imposed on the wave function in the path integral while the Sommerfeld quantization rule is derived by requiring that the state vector should be a single-valued function. The limitation of the semiclassical method is also clarified in terms of the square well and
δ(x) function potential models.
Two new Bohr-Sommerfeld (B-S) type quantization conditions for
d-dimensional radial potentials are proposed for non-singular and singular potentials, respectively. The power-like potentials \hbox{
V=sign(m)rm} for
m=−3/2,−1,−1/2,1,3,4,6 and
V=logr (that corresponds to
m=0) are studied in detail for radial quantum numbers
nr∈[0,100] and for angular momenta
ℓ=1,2,3,4,5 in dimensions
d=2,3. It is shown that for large
nr the B-S energies
EBS always tend to the exact ones. For
m=2 (the radial harmonic oscillator) and
m=−1 (the
d-dimensional analogue of the
3D Coulomb potential) the B-S spectrum coincides with the exact one for the first and second quantization conditions, respectively. In general, up to a small parametric shift of the radial quantum number, the analytic formulas for the energy spectrum can be written for arbitrary power-like potential. A comparison of
EBS with the energies
EBS(L), obtained for the radial potentials modified by the Langer correction for
d=3, are in good agreement in general: in detail, it was checked for the quartic oscillator
V=r4. It is demonstrated that introducing a dimensionless {\it WKB correction}
γ into the r.h.s. of the proposed B-S type quantization condition allows us to reproduce the exact energies with
γ being very small for positive degrees
m≥0 and sufficiently small for non-positive ones
m<0 for all
nr,ℓ studied.
A simple position probability density formulation is presented for the motion of a particle in a spherically symmetric potential. The approach provides an alternative to Newtonian methods for presentation in an elementary course, and requires only elementary algebra and one tabulated integral. The method is applied to compute the distributions for the Kepler-Coulomb and isotropic harmonic oscillator potentials. Formulas are also deduced for the average values for powers of the radial coordinate, and applied to describe perturbations to these systems. The classical results are also compared with quantum mechanical calculations using the Einstein-Brillouin-Keller semiclassical quantization.