Semiclassical bound-state quantization
For a one-dimensional smooth well with two separated simple turning points x₁<x₂ and decaying tails on both sides, leading WKB matching selects ∫_(x₁)^(x₂)√[2m(E_n−V)]dx≈πħ(n+½), n=0,1,… .
Key knowledge
For a one-dimensional smooth well with two separated simple turning points x₁<x₂ and decaying tails on both sides, leading WKB matching selects ∫_(x₁)^(x₂)√[2m(E_n−V)]dx≈πħ(n+½), n=0,1,… . A hard Dirichlet wall at x=0 with one soft turning point instead gives ∫_0^(x_t)k dx≈π(n+¾). Boundary type determines the phase offset.
Values and equations
∫_(x₁)^(x₂)p(x,E_n)dx≈πħ(n+½); p=√[2m(E_n−V)]
- x,x₁,x₂
- Position and turning-point positions m
- p
- Allowed local momentum kg m s⁻¹
- m
- Mass kg
- E_n,V
- Energy and potential energy J
- ħ
- Reduced Planck constant J s
- n
- Nonnegative integer
- k
- Allowed local wavenumber p/ħ m⁻¹
Conditions and scope
- Real smooth allowed interval, isolated simple turning points with Airy/WKB overlap, controlled semiclassical expansion, constant nonrelativistic mass and the specified bound-state boundary conditions.
- This is an approximation, not an exact spectrum for every well. Radial singularities, multiple wells, endpoint singularities and nearly merged turning points require appropriate modified matching.
Sources · 2
References
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Evidence and review
Quantum Physics III: chapter 6, adiabatic approximation (2017 notes, 2018 course): §1, printed page 4, equation 1.16: two-turning-point Bohr–Sommerfeld condition with n+1/2. Quantum Physics III: chapter 3, semiclassical approximation: §3.3 equations 3.3.6–3.3.7, printed pages 60–61: hard wall plus one soft point gives n+3/4; §3.4.2 equations 3.4.45–3.4.47 give the second soft-point phase. Does not infer the two-soft phase from the hard-wall formula.
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